From 0e61565b2bb5aa24da060b701378b22dee056312 Mon Sep 17 00:00:00 2001
From: Renato Atilio <renato@discourse.org>
Date: Tue, 4 Feb 2025 14:37:18 -0300
Subject: [PATCH] FEATURE: introduce a ProseMirror editor (#30815)

This is the first in a series of PRs to introduce a
ProseMirror-based
WYSIWYM editor experience
alongside our current textarea Markdown editor.

Behind a hidden site setting, this PR adds a toggle to the composer
toolbar, allowing users to switch between the two options.

Our implementation builds upon the excellent ProseMirror and its
non-core Markdown
module, using the
module's schema, parsing, and serialization definitions as the base for
further Discourse-specific features.

An extension API is included to enable further customizations.

The necessary extensions to support all Discourse's core and core
plugins features **will be implemented in subsequent PRs**.

---------

Co-authored-by: David Taylor <david@taylorhq.com>
---
 .../app/components/composer-container.hbs     |  34 +-
 .../app/components/composer-editor.hbs        |   3 +-
 .../app/components/composer-editor.js         |  27 +-
 .../components/composer/textarea-editor.gjs   |   2 +-
 .../app/components/composer/toggle-switch.gjs |  47 ++
 .../discourse/app/components/d-editor.hbs     |  13 +-
 .../discourse/app/components/d-editor.js      |  48 +-
 .../discourse/app/lib/autocomplete.js         |  61 ++-
 .../lib/composer/rich-editor-extensions.js    | 107 ++++
 .../app/lib/composer/text-manipulation.js     | 305 +++++++++++
 .../discourse/app/lib/intercept-click.js      |   1 +
 .../discourse/app/lib/load-rich-editor.js     |   5 +
 .../discourse/app/lib/plugin-api.gjs          |  14 +-
 .../app/lib/textarea-text-manipulation.js     |  44 +-
 .../discourse/app/lib/uppy/composer-upload.js |  18 +-
 .../discourse/app/services/composer.js        |  49 +-
 .../discourse/app/static/markdown-it/index.js |   2 +-
 .../components/prosemirror-editor.gjs         | 249 +++++++++
 .../app/static/prosemirror/core/inputrules.js | 128 +++++
 .../app/static/prosemirror/core/keymap.js     |  77 +++
 .../app/static/prosemirror/core/parser.js     |  84 +++
 .../app/static/prosemirror/core/plugin.js     |  49 ++
 .../app/static/prosemirror/core/schema.js     |  41 ++
 .../app/static/prosemirror/core/serializer.js |  36 ++
 .../prosemirror/extensions/placeholder.js     |  56 ++
 .../extensions/register-default.js            |  11 +
 .../app/static/prosemirror/lib/markdown-it.js |  27 +
 .../static/prosemirror/lib/plugin-utils.js    |   1 +
 .../prosemirror/lib/text-manipulation.js      | 490 ++++++++++++++++++
 app/assets/javascripts/discourse/package.json |  16 +-
 .../tests/helpers/rich-editor-helper.gjs      |  64 +++
 .../prosemirror-editor-test.gjs               | 203 ++++++++
 .../prosemirror-markdown-test.gjs             | 152 ++++++
 app/assets/stylesheets/common.scss            |   1 +
 .../stylesheets/common/components/_index.scss |   1 +
 .../components/composer-toggle-switch.scss    |  93 ++++
 .../common/rich-editor/_index.scss            |   1 +
 .../common/rich-editor/rich-editor.scss       | 256 +++++++++
 app/assets/stylesheets/mobile/compose.scss    |   1 +
 config/site_settings.yml                      |   4 +
 docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md       |   4 +
 jsconfig.json                                 |   1 +
 lib/svg_sprite.rb                             |   2 +
 .../discourse/components/chat-channel.gjs     |   6 +-
 .../initializers/chat-keyboard-shortcuts.js   |  10 +-
 pnpm-lock.yaml                                | 176 +++++++
 script/build_jsconfig.rb                      |   1 +
 .../composer/prosemirror_editor_spec.rb       | 290 +++++++++++
 .../page_objects/components/composer.rb       |  19 +
 49 files changed, 3200 insertions(+), 130 deletions(-)
 create mode 100644 app/assets/javascripts/discourse/app/components/composer/toggle-switch.gjs
 create mode 100644 app/assets/javascripts/discourse/app/lib/composer/rich-editor-extensions.js
 create mode 100644 app/assets/javascripts/discourse/app/lib/composer/text-manipulation.js
 create mode 100644 app/assets/javascripts/discourse/app/lib/load-rich-editor.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/components/prosemirror-editor.gjs
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/inputrules.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/keymap.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/parser.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/plugin.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/schema.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/core/serializer.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/extensions/placeholder.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/extensions/register-default.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/lib/markdown-it.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/lib/plugin-utils.js
 create mode 100644 app/assets/javascripts/discourse/app/static/prosemirror/lib/text-manipulation.js
 create mode 100644 app/assets/javascripts/discourse/tests/helpers/rich-editor-helper.gjs
 create mode 100644 app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-editor-test.gjs
 create mode 100644 app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-markdown-test.gjs
 create mode 100644 app/assets/stylesheets/common/components/composer-toggle-switch.scss
 create mode 100644 app/assets/stylesheets/common/rich-editor/_index.scss
 create mode 100644 app/assets/stylesheets/common/rich-editor/rich-editor.scss
 create mode 100644 spec/system/composer/prosemirror_editor_spec.rb

diff --git a/app/assets/javascripts/discourse/app/components/composer-container.hbs b/app/assets/javascripts/discourse/app/components/composer-container.hbs
index ca0002889a1..8995737599f 100644
--- a/app/assets/javascripts/discourse/app/components/composer-container.hbs
+++ b/app/assets/javascripts/discourse/app/components/composer-container.hbs
@@ -1,6 +1,6 @@
 <ComposerBody
   @composer={{this.composer.model}}
-  @showPreview={{this.composer.showPreview}}
+  @showPreview={{this.composer.isPreviewVisible}}
   @openIfDraft={{this.composer.openIfDraft}}
   @typed={{this.composer.typed}}
   @cancelled={{this.composer.cancelled}}
@@ -8,7 +8,7 @@
 >
   <div class="grippie"></div>
   {{#if this.composer.visible}}
-    {{html-class (if this.composer.showPreview "composer-has-preview")}}
+    {{html-class (if this.composer.isPreviewVisible "composer-has-preview")}}
     <ComposerMessages
       @composer={{this.composer.model}}
       @messageCount={{this.composer.messageCount}}
@@ -137,7 +137,7 @@
 
                 <div
                   class="title-and-category
-                    {{if this.composer.showPreview 'with-preview'}}"
+                    {{if this.composer.isPreviewVisible 'with-preview'}}"
                 >
                   <ComposerTitle
                     @composer={{this.composer.model}}
@@ -205,7 +205,7 @@
                   @connectorTagName="div"
                   @outletArgs={{hash
                     model=this.composer.model
-                    showPreview=this.composer.showPreview
+                    showPreview=this.composer.isPreviewVisible
                   }}
                 />
               </span>
@@ -295,17 +295,19 @@
               </a>
             {{/if}}
 
-            <a
-              href
-              class="btn btn-default no-text mobile-preview"
-              title={{i18n "composer.show_preview"}}
-              {{on "click" this.composer.togglePreview}}
-              aria-label={{i18n "composer.show_preview"}}
-            >
-              {{d-icon "desktop"}}
-            </a>
+            {{#if this.composer.allowPreview}}
+              <a
+                href
+                class="btn btn-default no-text mobile-preview"
+                title={{i18n "composer.show_preview"}}
+                {{on "click" this.composer.togglePreview}}
+                aria-label={{i18n "composer.show_preview"}}
+              >
+                {{d-icon "desktop"}}
+              </a>
+            {{/if}}
 
-            {{#if this.composer.showPreview}}
+            {{#if this.composer.isPreviewVisible}}
               <DButton
                 @action={{this.composer.togglePreview}}
                 @title="composer.hide_preview"
@@ -366,14 +368,14 @@
             {{/if}}
           </div>
 
-          {{#if this.site.desktopView}}
+          {{#if (and this.composer.allowPreview this.site.desktopView)}}
             <DButton
               @action={{this.composer.togglePreview}}
               @translatedTitle={{this.composer.toggleText}}
               @icon="angles-left"
               class={{concat-class
                 "btn-transparent btn-mini-toggle toggle-preview"
-                (unless this.composer.showPreview "active")
+                (unless this.composer.isPreviewVisible "active")
               }}
             />
           {{/if}}
diff --git a/app/assets/javascripts/discourse/app/components/composer-editor.hbs b/app/assets/javascripts/discourse/app/components/composer-editor.hbs
index a3ee48a7e35..4ae5c64a46b 100644
--- a/app/assets/javascripts/discourse/app/components/composer-editor.hbs
+++ b/app/assets/javascripts/discourse/app/components/composer-editor.hbs
@@ -30,8 +30,7 @@
     @previewUpdated={{action "previewUpdated"}}
     @markdownOptions={{this.markdownOptions}}
     @extraButtons={{action "extraButtons"}}
-    @importQuote={{this.composer.importQuote}}
-    @processPreview={{this.composer.showPreview}}
+    @processPreview={{this.composer.isPreviewVisible}}
     @validation={{this.validation}}
     @loading={{this.composer.loading}}
     @forcePreview={{this.forcePreview}}
diff --git a/app/assets/javascripts/discourse/app/components/composer-editor.js b/app/assets/javascripts/discourse/app/components/composer-editor.js
index 8e76b30d93e..d2887989cf3 100644
--- a/app/assets/javascripts/discourse/app/components/composer-editor.js
+++ b/app/assets/javascripts/discourse/app/components/composer-editor.js
@@ -194,17 +194,29 @@ export default class ComposerEditor extends Component {
     this.appEvents.trigger(`${this.composerEventPrefix}:will-open`);
   }
 
+  /**
+   * Sets up the editor with the given text manipulation instance
+   *
+   * @param {TextManipulation} textManipulation The text manipulation instance
+   * @returns {(() => void)} destructor function
+   */
   @bind
   setupEditor(textManipulation) {
     this.textManipulation = textManipulation;
-    this.uppyComposerUpload.textManipulation = textManipulation;
+    this.uppyComposerUpload.placeholderHandler = textManipulation.placeholder;
 
     const input = this.element.querySelector(".d-editor-input");
 
     input.addEventListener("scroll", this._throttledSyncEditorAndPreviewScroll);
 
-    // Focus on the body unless we have a title
-    if (!this.get("composer.model.canEditTitle")) {
+    this.composer.set("allowPreview", this.textManipulation.allowPreview);
+
+    if (
+      // Focus on the editor unless we have a title
+      !this.get("composer.model.canEditTitle") ||
+      // Or focus is in the body (e.g. when the editor is destroyed)
+      document.activeElement.tagName === "BODY"
+    ) {
       this.textManipulation.putCursorAtEnd();
     }
 
@@ -859,15 +871,6 @@ export default class ComposerEditor extends Component {
 
   @action
   extraButtons(toolbar) {
-    toolbar.addButton({
-      id: "quote",
-      group: "fontStyles",
-      icon: "far-comment",
-      sendAction: this.composer.importQuote,
-      title: "composer.quote_post_title",
-      unshift: true,
-    });
-
     if (
       this.composer.allowUpload &&
       this.composer.uploadIcon &&
diff --git a/app/assets/javascripts/discourse/app/components/composer/textarea-editor.gjs b/app/assets/javascripts/discourse/app/components/composer/textarea-editor.gjs
index beadea93fab..b1c635c37da 100644
--- a/app/assets/javascripts/discourse/app/components/composer/textarea-editor.gjs
+++ b/app/assets/javascripts/discourse/app/components/composer/textarea-editor.gjs
@@ -110,7 +110,7 @@ export default class TextareaEditor extends Component {
       @input={{@change}}
       @focusIn={{@focusIn}}
       @focusOut={{@focusOut}}
-      class="d-editor-input"
+      class={{@class}}
       @id={{@id}}
       {{this.registerTextarea}}
     />
diff --git a/app/assets/javascripts/discourse/app/components/composer/toggle-switch.gjs b/app/assets/javascripts/discourse/app/components/composer/toggle-switch.gjs
new file mode 100644
index 00000000000..bc60150123a
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/components/composer/toggle-switch.gjs
@@ -0,0 +1,47 @@
+import Component from "@glimmer/component";
+import { on } from "@ember/modifier";
+import { action } from "@ember/object";
+import concatClass from "discourse/helpers/concat-class";
+import icon from "discourse/helpers/d-icon";
+
+export default class ComposerToggleSwitch extends Component {
+  @action
+  mouseDown(event) {
+    if (this.args.preventFocus) {
+      event.preventDefault();
+    }
+  }
+
+  <template>
+    {{! template-lint-disable no-redundant-role }}
+    <button
+      class={{concatClass
+        "composer-toggle-switch"
+        (if @state "--rte" "--markdown")
+      }}
+      type="button"
+      role="switch"
+      aria-checked={{if @state "true" "false"}}
+      {{! template-lint-disable no-pointer-down-event-binding }}
+      {{on "mousedown" this.mouseDown}}
+      ...attributes
+    >
+      <span class="composer-toggle-switch__slider">
+        <span
+          class={{concatClass
+            "composer-toggle-switch__left-icon"
+            (unless @state "--active")
+          }}
+          aria-hidden="true"
+        >{{icon "fab-markdown"}}</span>
+        <span
+          class={{concatClass
+            "composer-toggle-switch__right-icon"
+            (if @state "--active")
+          }}
+          aria-hidden="true"
+        >{{icon "a"}}</span>
+      </span>
+    </button>
+  </template>
+}
diff --git a/app/assets/javascripts/discourse/app/components/d-editor.hbs b/app/assets/javascripts/discourse/app/components/d-editor.hbs
index 27a5f94ca07..8349bd32948 100644
--- a/app/assets/javascripts/discourse/app/components/d-editor.hbs
+++ b/app/assets/javascripts/discourse/app/components/d-editor.hbs
@@ -8,6 +8,14 @@
         {{if this.isEditorFocused 'in-focus'}}"
     >
       <div class="d-editor-button-bar" role="toolbar">
+        {{#if this.siteSettings.rich_editor}}
+          <Composer::ToggleSwitch
+            @preventFocus={{true}}
+            @state={{this.isRichEditorEnabled}}
+            {{on "click" this.toggleRichEditor}}
+          />
+        {{/if}}
+
         {{#each this.toolbar.groups as |group|}}
           {{#each group.buttons as |b|}}
             {{#if (b.condition this)}}
@@ -40,15 +48,18 @@
 
       <ConditionalLoadingSpinner @condition={{this.loading}} />
       <this.editorComponent
+        @class="d-editor-input"
         @onSetup={{this.setupEditor}}
         @markdownOptions={{this.markdownOptions}}
         @keymap={{this.keymap}}
         @value={{this.value}}
         @placeholder={{this.placeholderTranslated}}
         @disabled={{this.disabled}}
-        @change={{this.change}}
+        @change={{this.onChange}}
         @focusIn={{this.handleFocusIn}}
         @focusOut={{this.handleFocusOut}}
+        @categoryId={{@categoryId}}
+        @topicId={{@topicId}}
         @id={{this.textAreaId}}
       />
       <PopupInputTip @validation={{this.validation}} />
diff --git a/app/assets/javascripts/discourse/app/components/d-editor.js b/app/assets/javascripts/discourse/app/components/d-editor.js
index 68c3e2255c2..28a94be9f66 100644
--- a/app/assets/javascripts/discourse/app/components/d-editor.js
+++ b/app/assets/javascripts/discourse/app/components/d-editor.js
@@ -1,3 +1,4 @@
+import { tracked } from "@glimmer/tracking";
 import Component from "@ember/component";
 import { action } from "@ember/object";
 import { getOwner } from "@ember/owner";
@@ -26,6 +27,7 @@ import { wantsNewWindow } from "discourse/lib/intercept-click";
 import { PLATFORM_KEY_MODIFIER } from "discourse/lib/keyboard-shortcuts";
 import { linkSeenMentions } from "discourse/lib/link-mentions";
 import { loadOneboxes } from "discourse/lib/load-oneboxes";
+import loadRichEditor from "discourse/lib/load-rich-editor";
 import { findRawTemplate } from "discourse/lib/raw-templates";
 import { emojiUrlFor, generateCookFunction } from "discourse/lib/text";
 import userSearch from "discourse/lib/user-search";
@@ -59,8 +61,9 @@ export default class DEditor extends Component {
   @service modal;
   @service menu;
 
-  editorComponent = TextareaEditor;
-  textManipulation;
+  @tracked editorComponent;
+  /** @type {TextManipulation} */
+  @tracked textManipulation;
 
   ready = false;
   lastSel = null;
@@ -74,10 +77,19 @@ export default class DEditor extends Component {
     },
   };
 
-  init() {
+  async init() {
     super.init(...arguments);
 
     this.register = getRegister(this);
+
+    if (
+      this.siteSettings.rich_editor &&
+      this.keyValueStore.get("d-editor-prefers-rich-editor") === "true"
+    ) {
+      this.editorComponent = await loadRichEditor();
+    } else {
+      this.editorComponent = TextareaEditor;
+    }
   }
 
   @discourseComputed("placeholder")
@@ -630,9 +642,15 @@ export default class DEditor extends Component {
     this.set("isEditorFocused", false);
   }
 
+  /**
+   * Sets up the editor with the given text manipulation instance
+   *
+   * @param {TextManipulation} textManipulation The text manipulation instance
+   * @returns {(() => void)} destructor function
+   */
   @action
   setupEditor(textManipulation) {
-    this.set("textManipulation", textManipulation);
+    this.textManipulation = textManipulation;
 
     const destroyEvents = this.setupEvents();
 
@@ -657,6 +675,28 @@ export default class DEditor extends Component {
     };
   }
 
+  @action
+  async toggleRichEditor() {
+    this.editorComponent = this.isRichEditorEnabled
+      ? TextareaEditor
+      : await loadRichEditor();
+
+    this.keyValueStore.set({
+      key: "d-editor-prefers-rich-editor",
+      value: this.isRichEditorEnabled,
+    });
+  }
+
+  @action
+  onChange(event) {
+    this.set("value", event?.target?.value);
+    this.change?.(event);
+  }
+
+  get isRichEditorEnabled() {
+    return this.editorComponent !== TextareaEditor;
+  }
+
   setupEvents() {
     const textManipulation = this.textManipulation;
 
diff --git a/app/assets/javascripts/discourse/app/lib/autocomplete.js b/app/assets/javascripts/discourse/app/lib/autocomplete.js
index 9ef1508312f..247092ac9b8 100644
--- a/app/assets/javascripts/discourse/app/lib/autocomplete.js
+++ b/app/assets/javascripts/discourse/app/lib/autocomplete.js
@@ -114,6 +114,7 @@ export default function (options) {
   const isInput = me[0].tagName === "INPUT" && !options.treatAsTextarea;
   let inputSelectedItems = [];
 
+  /** @type {AutocompleteHandler} */
   options.textHandler ??= new TextareaAutocompleteHandler(me[0]);
 
   function handlePaste() {
@@ -249,14 +250,14 @@ export default function (options) {
               options.textHandler.getCaretPosition();
           }
 
-          options.textHandler.replaceTerm({
-            start: completeStart,
-            end: completeEnd,
-            term: (options.preserveKey ? options.key || "" : "") + term,
-          });
+          options.textHandler.replaceTerm(
+            completeStart,
+            completeEnd,
+            (options.preserveKey ? options.key || "" : "") + term
+          );
 
           if (options && options.afterComplete) {
-            options.afterComplete(options.textHandler.value, event);
+            options.afterComplete(options.textHandler.getValue(), event);
           }
         }
       }
@@ -481,7 +482,9 @@ export default function (options) {
     if (
       (term.length !== 0 && term.trim().length === 0) ||
       // close unless the caret is at the end of a word, like #line|<-
-      options.textHandler.value[options.textHandler.getCaretPosition()]?.trim()
+      options.textHandler
+        .getValue()
+        [options.textHandler.getCaretPosition()]?.trim()
     ) {
       closeAutocomplete();
       return null;
@@ -549,11 +552,11 @@ export default function (options) {
     }
 
     let cp = options.textHandler.getCaretPosition();
-    const key = options.textHandler.value[cp - 1];
+    const key = options.textHandler.getValue()[cp - 1];
 
     if (options.key) {
       if (options.onKeyUp && key !== options.key) {
-        let match = options.onKeyUp(options.textHandler.value, cp);
+        let match = options.onKeyUp(options.textHandler.getValue(), cp);
 
         if (match && (await checkTriggerRule())) {
           completeStart = cp - match[0].length;
@@ -565,7 +568,7 @@ export default function (options) {
 
     if (completeStart === null && cp > 0) {
       if (key === options.key) {
-        let prevChar = options.textHandler.value.charAt(cp - 2);
+        let prevChar = options.textHandler.getValue().charAt(cp - 2);
         if (
           (!prevChar || ALLOWED_LETTERS_REGEXP.test(prevChar)) &&
           (await checkTriggerRule())
@@ -575,11 +578,17 @@ export default function (options) {
         }
       }
     } else if (completeStart !== null) {
-      let term = options.textHandler.value.substring(
-        completeStart + (options.key ? 1 : 0),
-        cp
-      );
-      updateAutoComplete(dataSource(term, options));
+      let term = options.textHandler
+        .getValue()
+        .substring(completeStart + (options.key ? 1 : 0), cp);
+      if (
+        !options.key ||
+        options.textHandler.getValue()[completeStart] === options.key
+      ) {
+        updateAutoComplete(dataSource(term, options));
+      } else {
+        closeAutocomplete();
+      }
     }
   }
 
@@ -601,12 +610,12 @@ export default function (options) {
 
     while (prevIsGood && caretPos >= 0) {
       caretPos -= 1;
-      prev = options.textHandler.value[caretPos];
+      prev = options.textHandler.getValue()[caretPos];
 
       stopFound = prev === options.key;
 
       if (stopFound) {
-        prev = options.textHandler.value[caretPos - 1];
+        prev = options.textHandler.getValue()[caretPos - 1];
         const shouldTrigger = await checkTriggerRule({ backSpace });
 
         if (
@@ -614,10 +623,9 @@ export default function (options) {
           (prev === undefined || ALLOWED_LETTERS_REGEXP.test(prev))
         ) {
           start = caretPos;
-          term = options.textHandler.value.substring(
-            caretPos + 1,
-            initialCaretPos
-          );
+          term = options.textHandler
+            .getValue()
+            .substring(caretPos + 1, initialCaretPos);
           end = caretPos + term.length;
           break;
         }
@@ -648,7 +656,7 @@ export default function (options) {
           inputSelectedItems.push("");
         }
 
-        const value = options.textHandler.value;
+        const value = options.textHandler.getValue();
         if (typeof inputSelectedItems[0] === "string" && value.length > 0) {
           inputSelectedItems.pop();
           inputSelectedItems.push(value);
@@ -694,7 +702,7 @@ export default function (options) {
       // allow people to right arrow out of completion
       if (
         e.which === keys.rightArrow &&
-        options.textHandler.value[cp] === " "
+        options.textHandler.getValue()[cp] === " "
       ) {
         closeAutocomplete();
         return true;
@@ -770,10 +778,9 @@ export default function (options) {
             return true;
           }
 
-          term = options.textHandler.value.substring(
-            completeStart + (options.key ? 1 : 0),
-            cp
-          );
+          term = options.textHandler
+            .getValue()
+            .substring(completeStart + (options.key ? 1 : 0), cp);
 
           if (completeStart === cp && term === options.key) {
             closeAutocomplete();
diff --git a/app/assets/javascripts/discourse/app/lib/composer/rich-editor-extensions.js b/app/assets/javascripts/discourse/app/lib/composer/rich-editor-extensions.js
new file mode 100644
index 00000000000..2bc42fb595d
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/lib/composer/rich-editor-extensions.js
@@ -0,0 +1,107 @@
+// @ts-check
+
+/**
+ * @typedef PluginContext
+ * @property {string} placeholder
+ * @property {number} topicId
+ * @property {number} categoryId
+ * @property {import("discourse/models/session").default} session
+ */
+
+/**
+ * @typedef PluginParams
+ * @property {typeof import("discourse/static/prosemirror/lib/plugin-utils")} utils
+ * @property {typeof import('prosemirror-model')} pmModel
+ * @property {typeof import('prosemirror-view')} pmView
+ * @property {typeof import('prosemirror-state')} pmState
+ * @property {typeof import('prosemirror-history')} pmHistory
+ * @property {typeof import('prosemirror-transform')} pmTransform
+ * @property {typeof import('prosemirror-commands')} pmCommands
+ * @property {import('prosemirror-model').Schema} schema
+ * @property {() => PluginContext} getContext
+ */
+
+/** @typedef {import('prosemirror-state').PluginSpec} PluginSpec */
+/** @typedef {((params: PluginParams) => PluginSpec)} RichPluginFn */
+/** @typedef {PluginSpec | RichPluginFn} RichPlugin */
+
+/**
+ * @typedef InputRuleObject
+ * @property {RegExp} match
+ * @property {string | ((state: import('prosemirror-state').EditorState, match: RegExpMatchArray, start: number, end: number) => import('prosemirror-state').Transaction | null)} handler
+ * @property {{ undoable?: boolean, inCode?: boolean | "only" }} [options]
+ */
+
+/**
+ * @typedef InputRuleParams
+ * @property {import('prosemirror-model').Schema} schema
+ * @property {Function} markInputRule
+ */
+
+/** @typedef {((params: InputRuleParams) => InputRuleObject) | InputRuleObject} RichInputRule */
+
+// @ts-ignore we don't have type definitions for markdown-it
+/** @typedef {import("markdown-it").Token} MarkdownItToken */
+/** @typedef {(state: unknown, token: MarkdownItToken, tokenStream: MarkdownItToken[], index: number) => boolean | void} ParseFunction */
+/** @typedef {import("prosemirror-markdown").ParseSpec | ParseFunction} RichParseSpec */
+
+/**
+ * @typedef {(state: import("prosemirror-markdown").MarkdownSerializerState, node: import("prosemirror-model").Node, parent: import("prosemirror-model").Node, index: number) => void} SerializeNodeFn
+ */
+
+/** @typedef {Record<string, import('prosemirror-state').Command>} KeymapSpec */
+/** @typedef {((params: PluginParams) => KeymapSpec)} RichKeymapFn */
+/** @typedef {KeymapSpec | RichKeymapFn} RichKeymap */
+
+/**
+ * @typedef {Object} RichEditorExtension
+ * @property {Record<string, import('prosemirror-model').NodeSpec>} [nodeSpec]
+ *   Map containing Prosemirror node spec definitions, each key being the node name
+ *   See https://prosemirror.net/docs/ref/#model.NodeSpec
+ * @property {Record<string, import('prosemirror-model').MarkSpec>} [markSpec]
+ *   Map containing Prosemirror mark spec definitions, each key being the mark name
+ *   See https://prosemirror.net/docs/ref/#model.MarkSpec
+ * @property {RichInputRule | Array<RichInputRule>} [inputRules]
+ *   ProseMirror input rules. See https://prosemirror.net/docs/ref/#inputrules.InputRule
+ *   can be a function returning an array or an array of input rules
+ * @property {Record<string, SerializeNodeFn>} [serializeNode]
+ *   Node serialization definition
+ * @ts-ignore MarkSerializerSpec not currently exported
+ * @property {Record<string, import('prosemirror-markdown').MarkSerializerSpec>} [serializeMark]
+ *   Mark serialization definition
+ * @property {Record<string, RichParseSpec>} [parse]
+ *   Markdown-it token parse definition
+ * @property {RichPlugin | Array<RichPlugin>} [plugins]
+ *    ProseMirror plugins
+ * @property {Record<string, import('prosemirror-view').NodeViewConstructor>} [nodeViews]
+ *    ProseMirror node views
+ * @property {RichKeymap} [keymap]
+ *   Additional keymap definitions
+ */
+
+/** @type {RichEditorExtension[]} */
+const registeredExtensions = [];
+
+/**
+ * Registers an extension for the rich editor
+ *
+ * EXPERIMENTAL: This API will change without warning
+ *
+ * @param {RichEditorExtension} extension
+ */
+export function registerRichEditorExtension(extension) {
+  registeredExtensions.push(extension);
+}
+
+export function resetRichEditorExtensions() {
+  registeredExtensions.length = 0;
+}
+
+/**
+ * Get all extensions registered for the rich editor
+ *
+ * @returns {RichEditorExtension[]}
+ */
+export function getExtensions() {
+  return registeredExtensions;
+}
diff --git a/app/assets/javascripts/discourse/app/lib/composer/text-manipulation.js b/app/assets/javascripts/discourse/app/lib/composer/text-manipulation.js
new file mode 100644
index 00000000000..4a81c39f7c9
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/lib/composer/text-manipulation.js
@@ -0,0 +1,305 @@
+// @ts-check
+
+/**
+ * Interface for text manipulation with an underlying editor implementation.
+ *
+ * @interface TextManipulation
+ */
+export const TextManipulation = {};
+
+/**
+ * Whether the editor allows a preview being shown
+ * @name TextManipulation#allowPreview
+ * @type {boolean}
+ * @readonly
+ */
+
+/**
+ * Focuses the editor
+ *
+ * @method
+ * @name TextManipulation#focus
+ * @returns {void}
+ */
+
+/**
+ * Blurs and focuses the editor
+ *
+ * @method
+ * @name TextManipulation#blurAndFocus
+ * @returns {void}
+ */
+
+/**
+ * Indents/un-indents the current selection
+ *
+ * @method
+ * @name TextManipulation#indentSelection
+ * @param {string} direction The direction to indent in. Either "right" or "left"
+ * @returns {void}
+ */
+
+/**
+ * Configures an Autocomplete for the editor
+ *
+ * @method
+ * @name TextManipulation#autocomplete
+ * @param {unknown} options The options for the jQuery autocomplete
+ * @returns {void}
+ */
+
+/**
+ * Checks if the current selection is in a code block
+ *
+ * @method
+ * @name TextManipulation#inCodeBlock
+ * @returns {Promise<boolean>}
+ */
+
+/**
+ * Gets the current selection
+ *
+ * @method
+ * @name TextManipulation#getSelected
+ * @param {unknown} trimLeading
+ * @returns {unknown}
+ */
+
+/**
+ * Selects the text from the given range
+ *
+ * @method
+ * @name TextManipulation#selectText
+ * @param {number} from
+ * @param {number} to
+ * @param {unknown} [options]
+ * @returns {void}
+ */
+
+/**
+ * Applies the given head/tail to the selected text
+ *
+ * @method
+ * @name TextManipulation#applySurround
+ * @param {string} selected The selected text
+ * @param {string} head The text to be inserted before the selection
+ * @param {string} tail The text to be inserted after the selection
+ * @param {string} exampleKey The key of the example
+ * @param {unknown} [opts]
+ */
+
+/**
+ * Applies the list format to the selected text
+ *
+ * @method
+ * @name TextManipulation#applyList
+ * @param {string} selected The selected text
+ * @param {string} head The text to be inserted before the selection
+ * @param {string} exampleKey The key of the example
+ * @param {unknown} [opts]
+ */
+
+/**
+ * Formats the current selection as code
+ *
+ * @method
+ * @name TextManipulation#formatCode
+ * @returns {void}
+ */
+
+/**
+ * Adds text
+ *
+ * @method
+ * @name TextManipulation#addText
+ * @param {string} selected The selected text
+ * @param {string} text The text to be inserted
+ */
+
+/**
+ * Toggles the text (LTR/RTL) direction
+ *
+ * @method
+ * @name TextManipulation#toggleDirection
+ * @returns {void}
+ */
+
+/**
+ * Replaces text
+ *
+ * @method
+ * @name TextManipulation#replaceText
+ * @param {string} oldValue The old value
+ * @param {string} newValue The new value
+ * @param {unknown} [opts]
+ * @returns {void}
+ */
+
+/**
+ * Handles the paste event
+ *
+ * @method
+ * @name TextManipulation#paste
+ * @param {ClipboardEvent} event The paste event
+ * @returns {void}
+ */
+
+/**
+ * Inserts the block
+ *
+ * @method
+ * @name TextManipulation#insertBlock
+ * @param {string} block The block to be inserted
+ * @returns {void}
+ */
+
+/**
+ * Inserts text
+ *
+ * @method
+ * @name TextManipulation#insertText
+ * @param {string} text The text to be inserted
+ * @returns {void}
+ */
+
+/**
+ * Applies the head/tail to the selected text
+ *
+ * @method
+ * @name TextManipulation#applySurroundSelection
+ * @param {string} head The text to be inserted before the selection
+ * @param {string} tail The text to be inserted after the selection
+ * @param {string} exampleKey The key of the example
+ * @param {unknown} [opts]
+ * @returns {void}
+ */
+
+/**
+ * Puts cursor at the end of the editor
+ *
+ * @method
+ * @name TextManipulation#putCursorAtEnd
+ * @returns {void}
+ */
+
+/**
+ * The placeholder handler instance
+ *
+ * @name TextManipulation#placeholder
+ * @type {PlaceholderHandler}
+ * @readonly
+ */
+
+/** @typedef {import("@uppy/utils/lib/UppyFile").MinimalRequiredUppyFile<any,any>} UppyFile */
+
+/**
+ * Interface for handling placeholders on upload events
+ *
+ * @interface PlaceholderHandler
+ */
+export const PlaceholderHandler = {};
+
+/**
+ * Inserts a file
+ *
+ * @method
+ * @name PlaceholderHandler#insert
+ * @param {UppyFile} file The uploaded file
+ * @returns {void}
+ */
+
+/**
+ * Success event for file upload
+ *
+ * @method
+ * @name PlaceholderHandler#success
+ * @param {UppyFile} file The uploaded file
+ * @param {string} markdown The markdown for the uploaded file
+ * @returns {void}
+ */
+
+/**
+ * Cancels all uploads
+ *
+ * @method
+ * @name PlaceholderHandler#cancelAll
+ * @returns {void}
+ */
+
+/**
+ * Cancels one uploaded file
+ *
+ * @method
+ * @name PlaceholderHandler#cancel
+ * @param {UppyFile} file The uploaded file
+ * @returns {void}
+ */
+
+/**
+ * Progress event
+ *
+ * @method
+ * @name PlaceholderHandler#progress
+ * @param {UppyFile} file The uploaded file
+ * @returns {void}
+ */
+
+/**
+ * Progress complete event
+ *
+ * @method
+ * @name PlaceholderHandler#progressComplete
+ * @param {UppyFile} file The uploaded file
+ * @returns {void}
+ */
+
+/**
+ * Interface for the Autocomplete handler
+ *
+ * @interface AutocompleteHandler
+ */
+export const AutocompleteHandler = {};
+
+/**
+ * Replaces the range with the given text
+ *
+ * @method
+ * @name AutocompleteHandler#replaceTerm
+ * @param {number} start The start of the range
+ * @param {number} end The end of the range
+ * @param {string} text The text to be inserted
+ * @returns {void}
+ */
+
+/**
+ * Gets the caret position
+ *
+ * @method
+ * @name AutocompleteHandler#getCaretPosition
+ * @returns {number}
+ */
+
+/**
+ * Checks if the current selection is in a code block
+ *
+ * @method
+ * @name AutocompleteHandler#inCodeBlock
+ * @returns {Promise<boolean>}
+ */
+
+/**
+ * Gets the caret coordinates
+ *
+ * @method
+ * @name AutocompleteHandler#getCaretCoords
+ * @param {number} caretPositon The caret position to get the coords for
+ * @returns {{ top: number, left: number }}
+ */
+
+/**
+ * Gets the current value for the autocomplete
+ *
+ * @method
+ * @name AutocompleteHandler#getValue
+ * @returns {string}
+ */
diff --git a/app/assets/javascripts/discourse/app/lib/intercept-click.js b/app/assets/javascripts/discourse/app/lib/intercept-click.js
index da15dfd60b3..d8fb98af66b 100644
--- a/app/assets/javascripts/discourse/app/lib/intercept-click.js
+++ b/app/assets/javascripts/discourse/app/lib/intercept-click.js
@@ -48,6 +48,7 @@ export default function interceptClick(e) {
       target.classList.contains("ember-view")) ||
     target.classList.contains("lightbox") ||
     href.startsWith("mailto:") ||
+    target.closest('[contenteditable="true"]') ||
     (href.match(/^http[s]?:\/\//i) &&
       !href.match(new RegExp("^https?:\\/\\/" + window.location.hostname, "i")))
   ) {
diff --git a/app/assets/javascripts/discourse/app/lib/load-rich-editor.js b/app/assets/javascripts/discourse/app/lib/load-rich-editor.js
new file mode 100644
index 00000000000..046404e3c85
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/lib/load-rich-editor.js
@@ -0,0 +1,5 @@
+export default async function loadRichEditor() {
+  return (
+    await import("discourse/static/prosemirror/components/prosemirror-editor")
+  ).default;
+}
diff --git a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
index ecd97ae01f4..f556974cf60 100644
--- a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
+++ b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
@@ -3,7 +3,7 @@
 // docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md whenever you change the version
 // using the format described at https://keepachangelog.com/en/1.0.0/.
 
-export const PLUGIN_API_VERSION = "2.0.1";
+export const PLUGIN_API_VERSION = "2.1.0";
 
 import $ from "jquery";
 import { h } from "virtual-dom";
@@ -66,6 +66,7 @@ import classPrepend, {
   withPrependsRolledBack,
 } from "discourse/lib/class-prepend";
 import { addPopupMenuOption } from "discourse/lib/composer/custom-popup-menu-options";
+import { registerRichEditorExtension } from "discourse/lib/composer/rich-editor-extensions";
 import deprecated from "discourse/lib/deprecated";
 import { registerDesktopNotificationHandler } from "discourse/lib/desktop-notifications";
 import { downloadCalendar } from "discourse/lib/download-calendar";
@@ -3389,6 +3390,17 @@ class PluginApi {
     registerReportModeComponent(mode, componentClass);
   }
 
+  /**
+   * Registers an extension for the rich editor
+   *
+   * EXPERIMENTAL: This API will change without warning
+   *
+   * @param {RichEditorExtension} extension
+   */
+  registerRichEditorExtension(extension) {
+    registerRichEditorExtension(extension);
+  }
+
   #deprecatedWidgetOverride(widgetName, override) {
     // insert here the code to handle widget deprecations, e.g. for the header widgets we used:
     // if (DEPRECATED_HEADER_WIDGETS.includes(widgetName)) {
diff --git a/app/assets/javascripts/discourse/app/lib/textarea-text-manipulation.js b/app/assets/javascripts/discourse/app/lib/textarea-text-manipulation.js
index 880df0a7969..c290d0de0c3 100644
--- a/app/assets/javascripts/discourse/app/lib/textarea-text-manipulation.js
+++ b/app/assets/javascripts/discourse/app/lib/textarea-text-manipulation.js
@@ -1,5 +1,6 @@
+// @ts-check
 import { setOwner } from "@ember/owner";
-import { schedule } from "@ember/runloop";
+import { next, schedule } from "@ember/runloop";
 import { service } from "@ember/service";
 import { isEmpty } from "@ember/utils";
 import $ from "jquery";
@@ -19,6 +20,12 @@ import {
 } from "discourse/lib/utilities";
 import { i18n } from "discourse-i18n";
 
+/**
+ * @typedef {import("discourse/lib/composer/text-manipulation").TextManipulation} TextManipulation
+ * @typedef {import("discourse/lib/composer/text-manipulation").AutocompleteHandler} AutocompleteHandler
+ * @typedef {import("discourse/lib/composer/text-manipulation").PlaceholderHandler} PlaceholderHandler
+ */
+
 const INDENT_DIRECTION_LEFT = "left";
 const INDENT_DIRECTION_RIGHT = "right";
 
@@ -33,9 +40,13 @@ const OP = {
 
 const FOUR_SPACES_INDENT = "4-spaces-indent";
 
-// Our head can be a static string or a function that returns a string
-// based on input (like for numbered lists).
-export function getHead(head, prev) {
+/**
+ * Our head can be a static string or a function that returns a string
+ * based on input (like for numbered lists).
+ *
+ * @returns {[string, number]}
+ */
+function getHead(head, prev) {
   if (typeof head === "string") {
     return [head, head.length];
   } else {
@@ -43,12 +54,15 @@ export function getHead(head, prev) {
   }
 }
 
+/** @implements {TextManipulation} */
 export default class TextareaTextManipulation {
   @service appEvents;
   @service siteSettings;
   @service capabilities;
   @service currentUser;
 
+  allowPreview = true;
+
   eventPrefix;
   textarea;
   $textarea;
@@ -816,11 +830,18 @@ export default class TextareaTextManipulation {
   }
 
   putCursorAtEnd() {
-    putCursorAtEnd(this.textarea);
+    if (this.capabilities.isIOS) {
+      putCursorAtEnd(this.textarea);
+    } else {
+      // in some browsers, the focus() called by putCursorAtEnd doesn't bubble the event to set
+      // isEditorFoused=true and bring the focus indicator to the wrapper, unless we do it on next tick
+      next(() => putCursorAtEnd(this.textarea));
+    }
   }
 
   autocomplete(options) {
-    return this.$textarea.autocomplete(
+    // @ts-ignore
+    this.$textarea.autocomplete(
       options instanceof Object
         ? { textHandler: this.autocompleteHandler, ...options }
         : options
@@ -838,6 +859,7 @@ function insertAtTextarea(textarea, start, end, text) {
   }
 }
 
+/** @implements {AutocompleteHandler} */
 export class TextareaAutocompleteHandler {
   textarea;
   $textarea;
@@ -847,12 +869,13 @@ export class TextareaAutocompleteHandler {
     this.$textarea = $(textarea);
   }
 
-  get value() {
+  getValue() {
     return this.textarea.value;
   }
 
-  replaceTerm({ start, end, term }) {
-    const space = this.value.substring(end + 1, end + 2) === " " ? "" : " ";
+  replaceTerm(start, end, term) {
+    const space =
+      this.getValue().substring(end + 1, end + 2) === " " ? "" : " ";
     insertAtTextarea(this.textarea, start, end + 1, term + space);
     setCaretPosition(this.textarea, start + 1 + term.trim().length);
   }
@@ -862,6 +885,7 @@ export class TextareaAutocompleteHandler {
   }
 
   getCaretCoords(start) {
+    // @ts-ignore
     return this.$textarea.caretPosition({ pos: start + 1 });
   }
 
@@ -873,9 +897,11 @@ export class TextareaAutocompleteHandler {
   }
 }
 
+/** @implements {PlaceholderHandler} */
 class TextareaPlaceholderHandler {
   @service composer;
 
+  /** @type {TextareaTextManipulation} */
   textManipulation;
 
   #placeholders = {};
diff --git a/app/assets/javascripts/discourse/app/lib/uppy/composer-upload.js b/app/assets/javascripts/discourse/app/lib/uppy/composer-upload.js
index 6d66eff3460..a56ed7a5bee 100644
--- a/app/assets/javascripts/discourse/app/lib/uppy/composer-upload.js
+++ b/app/assets/javascripts/discourse/app/lib/uppy/composer-upload.js
@@ -52,7 +52,8 @@ export default class UppyComposerUpload {
   uploadPreProcessors;
   uploadHandlers;
 
-  textManipulation;
+  /** @type {PlaceholderHandler} */
+  placeholderHandler;
 
   #inProgressUploads = [];
   #bufferedUploadErrors = [];
@@ -334,7 +335,7 @@ export default class UppyComposerUpload {
             })
           );
 
-          this.textManipulation.placeholder.insert(file);
+          this.placeholderHandler.insert(file);
 
           this.appEvents.trigger(
             `${this.composerEventPrefix}:upload-started`,
@@ -369,7 +370,7 @@ export default class UppyComposerUpload {
           file,
           upload.url,
           () => {
-            this.textManipulation.placeholder.success(file, markdown);
+            this.placeholderHandler.success(file, markdown);
 
             this.appEvents.trigger(
               `${this.composerEventPrefix}:upload-success`,
@@ -395,7 +396,7 @@ export default class UppyComposerUpload {
     this.uppyWrapper.uppyInstance.on("cancel-all", () => {
       // Do the manual cancelling work only if the user clicked cancel
       if (this.#userCancelled) {
-        this.textManipulation.placeholder.cancelAll();
+        this.placeholderHandler.cancelAll();
         this.#userCancelled = false;
         this.#reset();
 
@@ -480,13 +481,13 @@ export default class UppyComposerUpload {
       });
 
     this.uppyWrapper.onPreProcessProgress((file) => {
-      this.textManipulation.placeholder.progress(file);
+      this.placeholderHandler.progress(file);
     });
 
     this.uppyWrapper.onPreProcessComplete(
       (file) => {
         run(() => {
-          this.textManipulation.placeholder.progressComplete(file);
+          this.placeholderHandler.progressComplete(file);
         });
       },
       () => {
@@ -529,13 +530,13 @@ export default class UppyComposerUpload {
   }
 
   #resetUpload(file) {
-    this.textManipulation.placeholder.cancel(file);
+    this.placeholderHandler.cancel(file);
   }
 
   @bind
   _pasteEventListener(event) {
     if (
-      document.activeElement !== document.querySelector(this.editorInputClass)
+      !document.querySelector(this.editorInputClass)?.contains(event.target)
     ) {
       return;
     }
@@ -550,6 +551,7 @@ export default class UppyComposerUpload {
     }
 
     if (event && event.clipboardData && event.clipboardData.files) {
+      event.preventDefault();
       this._addFiles([...event.clipboardData.files], { pasted: true });
     }
   }
diff --git a/app/assets/javascripts/discourse/app/services/composer.js b/app/assets/javascripts/discourse/app/services/composer.js
index 72e874009b7..f532483beb1 100644
--- a/app/assets/javascripts/discourse/app/services/composer.js
+++ b/app/assets/javascripts/discourse/app/services/composer.js
@@ -1,3 +1,4 @@
+import { tracked } from "@glimmer/tracking";
 import EmberObject, { action, computed } from "@ember/object";
 import { alias, and, or, reads } from "@ember/object/computed";
 import { cancel, scheduleOnce } from "@ember/runloop";
@@ -27,7 +28,6 @@ import { getOwnerWithFallback } from "discourse/lib/get-owner";
 import getURL from "discourse/lib/get-url";
 import { disableImplicitInjections } from "discourse/lib/implicit-injections";
 import { wantsNewWindow } from "discourse/lib/intercept-click";
-import { buildQuote } from "discourse/lib/quote";
 import { emojiUnescape } from "discourse/lib/text";
 import {
   authorizesOneOrMoreExtensions,
@@ -106,6 +106,8 @@ export default class ComposerService extends Service {
   @service siteSettings;
   @service store;
 
+  @tracked showPreview = true;
+  @tracked allowPreview = true;
   checkedMessages = false;
   messageCount = null;
   showEditReason = false;
@@ -119,7 +121,7 @@ export default class ComposerService extends Service {
   uploadProgress;
   topic = null;
   linkLookup = null;
-  showPreview = true;
+
   composerHeight = null;
 
   @and("site.mobileView", "showPreview") forcePreview;
@@ -135,6 +137,10 @@ export default class ComposerService extends Service {
     return getOwnerWithFallback(this).lookup("controller:topic");
   }
 
+  get isPreviewVisible() {
+    return this.showPreview && this.allowPreview;
+  }
+
   get isOpen() {
     return this.model?.composeState === Composer.OPEN;
   }
@@ -841,45 +847,6 @@ export default class ComposerService extends Service {
     return false;
   }
 
-  // Import a quote from the post
-  @action
-  async importQuote(toolbarEvent) {
-    const postStream = this.get("topic.postStream");
-    let postId = this.get("model.post.id");
-
-    // If there is no current post, use the first post id from the stream
-    if (!postId && postStream) {
-      postId = postStream.get("stream.firstObject");
-    }
-
-    // If we're editing a post, fetch the reply when importing a quote
-    if (this.get("model.editingPost")) {
-      const replyToPostNumber = this.get("model.post.reply_to_post_number");
-      if (replyToPostNumber) {
-        const replyPost = postStream.posts.findBy(
-          "post_number",
-          replyToPostNumber
-        );
-
-        if (replyPost) {
-          postId = replyPost.id;
-        }
-      }
-    }
-
-    if (!postId) {
-      return;
-    }
-
-    this.set("model.loading", true);
-
-    const post = await this.store.find("post", postId);
-    const quote = buildQuote(post, post.raw, { full: true });
-
-    toolbarEvent.addText(quote);
-    this.set("model.loading", false);
-  }
-
   @action
   saveAction(ignore, event) {
     this.save(false, {
diff --git a/app/assets/javascripts/discourse/app/static/markdown-it/index.js b/app/assets/javascripts/discourse/app/static/markdown-it/index.js
index c460fcd09e3..127d23b7a20 100644
--- a/app/assets/javascripts/discourse/app/static/markdown-it/index.js
+++ b/app/assets/javascripts/discourse/app/static/markdown-it/index.js
@@ -4,7 +4,7 @@ import loadPluginFeatures from "./features";
 import MentionsParser from "./mentions-parser";
 import buildOptions from "./options";
 
-function buildEngine(options) {
+export function buildEngine(options) {
   return DiscourseMarkdownIt.withCustomFeatures(
     loadPluginFeatures()
   ).withOptions(buildOptions(options));
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/components/prosemirror-editor.gjs b/app/assets/javascripts/discourse/app/static/prosemirror/components/prosemirror-editor.gjs
new file mode 100644
index 00000000000..91b5578f340
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/components/prosemirror-editor.gjs
@@ -0,0 +1,249 @@
+// @ts-check
+import Component from "@glimmer/component";
+import { action } from "@ember/object";
+import { getOwner } from "@ember/owner";
+import didInsert from "@ember/render-modifiers/modifiers/did-insert";
+import didUpdate from "@ember/render-modifiers/modifiers/did-update";
+import willDestroy from "@ember/render-modifiers/modifiers/will-destroy";
+import { next } from "@ember/runloop";
+import { service } from "@ember/service";
+import "../extensions/register-default";
+import { baseKeymap } from "prosemirror-commands";
+import * as ProsemirrorCommands from "prosemirror-commands";
+import { dropCursor } from "prosemirror-dropcursor";
+import { gapCursor } from "prosemirror-gapcursor";
+import * as ProsemirrorHistory from "prosemirror-history";
+import { history } from "prosemirror-history";
+import { keymap } from "prosemirror-keymap";
+import * as ProsemirrorModel from "prosemirror-model";
+import * as ProsemirrorState from "prosemirror-state";
+import { EditorState } from "prosemirror-state";
+import * as ProsemirrorTransform from "prosemirror-transform";
+import * as ProsemirrorView from "prosemirror-view";
+import { EditorView } from "prosemirror-view";
+import { getExtensions } from "discourse/lib/composer/rich-editor-extensions";
+import { bind } from "discourse/lib/decorators";
+import { buildInputRules } from "../core/inputrules";
+import { buildKeymap } from "../core/keymap";
+import Parser from "../core/parser";
+import { extractNodeViews, extractPlugins } from "../core/plugin";
+import { createSchema } from "../core/schema";
+import Serializer from "../core/serializer";
+import placeholder from "../extensions/placeholder";
+import * as utils from "../lib/plugin-utils";
+import TextManipulation from "../lib/text-manipulation";
+
+const AUTOCOMPLETE_KEY_DOWN_SUPPRESS = ["Enter", "Tab"];
+
+/**
+ * @typedef ProsemirrorEditorArgs
+ * @property {string} [value] The markdown content to be rendered in the editor
+ * @property {string} [placeholder] The placeholder text to be displayed when the editor is empty
+ * @property {boolean} [disabled] Whether the editor should be disabled
+ * @property {Record<string, () => void>} [keymap] A mapping of keybindings to commands
+ * @property {(value: { target: { value: string } }) => void} [change] A callback called when the editor content changes
+ * @property {() => void} [focusIn] A callback called when the editor gains focus
+ * @property {() => void} [focusOut] A callback called when the editor loses focus
+ * @property {(textManipulation: TextManipulation) => undefined | (() => void)} [onSetup] A callback called when the editor is set up, may return a destructor
+ * @property {number} [topicId] The ID of the topic being edited, if any
+ * @property {number} [categoryId] The ID of the category of the topic being edited, if any
+ * @property {string} [class] The class to be added to the ProseMirror contentEditable editor
+ * @property {boolean} [includeDefault] If default node and mark spec/parse/serialize/inputRules definitions from ProseMirror should be included
+ * @property {import("discourse/lib/composer/rich-editor-extensions").RichEditorExtension[]} [extensions] A list of extensions to be used with the editor INSTEAD of the ones registered through the API
+ */
+
+/**
+ * @typedef ProsemirrorEditorSignature
+ * @property {ProsemirrorEditorArgs} Args
+ */
+
+/**
+ * @extends {Component<ProsemirrorEditorSignature>}
+ */
+export default class ProsemirrorEditor extends Component {
+  @service session;
+  @service dialog;
+
+  schema = createSchema(this.extensions, this.args.includeDefault);
+  view;
+
+  #lastSerialized;
+  /** @type {undefined | (() => void)} */
+  #destructor;
+
+  get pluginParams() {
+    return {
+      utils,
+      schema: this.schema,
+      pmState: ProsemirrorState,
+      pmModel: ProsemirrorModel,
+      pmView: ProsemirrorView,
+      pmHistory: ProsemirrorHistory,
+      pmTransform: ProsemirrorTransform,
+      pmCommands: ProsemirrorCommands,
+      getContext: () => ({
+        placeholder: this.args.placeholder,
+        topicId: this.args.topicId,
+        categoryId: this.args.categoryId,
+        session: this.session,
+      }),
+    };
+  }
+
+  get extensions() {
+    const extensions = this.args.extensions ?? getExtensions();
+
+    // enforcing core extensions
+    return extensions.includes(placeholder)
+      ? extensions
+      : [placeholder, ...extensions];
+  }
+
+  get keymapFromArgs() {
+    const replacements = { tab: "Tab" };
+    const result = {};
+    for (const [key, value] of Object.entries(this.args.keymap ?? {})) {
+      const pmKey = key
+        .split("+")
+        .map((word) => replacements[word] ?? word)
+        .join("-");
+      result[pmKey] = value;
+    }
+    return result;
+  }
+
+  @action
+  handleAsyncPlugin(plugin) {
+    const state = this.view.state.reconfigure({
+      plugins: [...this.view.state.plugins, plugin],
+    });
+
+    this.view.updateState(state);
+  }
+
+  @action
+  setup(container) {
+    const params = this.pluginParams;
+
+    const plugins = [
+      buildInputRules(this.extensions, this.schema, this.args.includeDefault),
+      keymap(
+        buildKeymap(
+          this.extensions,
+          this.schema,
+          this.keymapFromArgs,
+          params,
+          this.args.includeDefault
+        )
+      ),
+      keymap(baseKeymap),
+      dropCursor({ color: "var(--primary)" }),
+      gapCursor(),
+      history(),
+      ...extractPlugins(this.extensions, params, this.handleAsyncPlugin),
+    ];
+
+    this.parser = new Parser(this.extensions, this.args.includeDefault);
+    this.serializer = new Serializer(this.extensions, this.args.includeDefault);
+
+    const state = EditorState.create({ schema: this.schema, plugins });
+
+    this.view = new EditorView(container, {
+      state,
+      nodeViews: extractNodeViews(this.extensions),
+      attributes: { class: this.args.class },
+      editable: () => this.args.disabled !== true,
+      dispatchTransaction: (tr) => {
+        this.view.updateState(this.view.state.apply(tr));
+
+        if (tr.docChanged && tr.getMeta("addToHistory") !== false) {
+          // If this gets expensive, we can debounce it
+          const value = this.serializer.convert(this.view.state.doc);
+          this.#lastSerialized = value;
+          this.args.change?.({ target: { value } });
+        }
+      },
+      handleDOMEvents: {
+        focus: () => {
+          this.args.focusIn?.();
+          return false;
+        },
+        blur: () => {
+          next(() => this.args.focusOut?.());
+          return false;
+        },
+      },
+      handleKeyDown: (view, event) => {
+        // suppress if Enter/Tab and the autocomplete is open
+        return (
+          AUTOCOMPLETE_KEY_DOWN_SUPPRESS.includes(event.key) &&
+          !!document.querySelector(".autocomplete")
+        );
+      },
+    });
+
+    this.textManipulation = new TextManipulation(getOwner(this), {
+      schema: this.schema,
+      view: this.view,
+      convertFromMarkdown: this.convertFromMarkdown,
+      convertToMarkdown: this.serializer.convert.bind(this.serializer),
+    });
+
+    this.#destructor = this.args.onSetup?.(this.textManipulation);
+
+    this.convertFromValue();
+  }
+
+  @bind
+  convertFromMarkdown(markdown) {
+    try {
+      return this.parser.convert(this.schema, markdown);
+    } catch (e) {
+      next(() => this.dialog.alert(e.message));
+      throw e;
+    }
+  }
+
+  @bind
+  convertFromValue() {
+    // Ignore the markdown we just serialized
+    if (this.args.value === this.#lastSerialized) {
+      return;
+    }
+
+    const doc = this.convertFromMarkdown(this.args.value);
+
+    const tr = this.view.state.tr;
+    tr.replaceWith(0, this.view.state.doc.content.size, doc.content).setMeta(
+      "addToHistory",
+      false
+    );
+    this.view.updateState(this.view.state.apply(tr));
+  }
+
+  @action
+  teardown() {
+    this.#destructor?.();
+    this.view.destroy();
+  }
+
+  @action
+  updateContext(element, [key, value]) {
+    this.view.dispatch(
+      this.view.state.tr
+        .setMeta("addToHistory", false)
+        .setMeta("discourseContextChanged", { key, value })
+    );
+  }
+
+  <template>
+    <div
+      class="ProseMirror-container"
+      {{didInsert this.setup}}
+      {{didUpdate this.convertFromValue @value}}
+      {{didUpdate this.updateContext "placeholder" @placeholder}}
+      {{willDestroy this.teardown}}
+    >
+    </div>
+  </template>
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/inputrules.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/inputrules.js
new file mode 100644
index 00000000000..cafe437fd2d
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/inputrules.js
@@ -0,0 +1,128 @@
+import {
+  InputRule,
+  inputRules,
+  smartQuotes,
+  textblockTypeInputRule,
+  wrappingInputRule,
+} from "prosemirror-inputrules";
+
+export function buildInputRules(extensions, schema, includeDefault = true) {
+  const rules = [];
+
+  if (includeDefault) {
+    rules.push(
+      // TODO(renato) smartQuotes should respect `markdown_typographer_quotation_marks`
+      ...smartQuotes,
+      ...[
+        wrappingInputRule(/^\s*>\s$/, schema.nodes.blockquote),
+
+        orderedListRule(schema.nodes.ordered_list),
+        bulletListRule(schema.nodes.bullet_list),
+
+        textblockTypeInputRule(/^```$/, schema.nodes.code_block),
+        textblockTypeInputRule(/^ {4}$/, schema.nodes.code_block),
+
+        headingRule(schema.nodes.heading, 6),
+
+        markInputRule(/\*\*([^*]+)\*\*$/, schema.marks.strong),
+        markInputRule(/(?<=^|\s)__([^_]+)__$/, schema.marks.strong),
+        markInputRule(/(?:^|(?<!\*))\*([^*]+)\*$/, schema.marks.em),
+        markInputRule(/(?<=^|\s)_([^_]+)_$/, schema.marks.em),
+        markInputRule(/`([^`]+)`$/, schema.marks.code),
+      ]
+    );
+  }
+
+  rules.push(...extractInputRules(extensions, schema));
+
+  return inputRules({ rules });
+}
+
+function extractInputRules(extensions, schema) {
+  return extensions.flatMap(({ inputRules: extensionRules }) =>
+    extensionRules ? processInputRule(extensionRules, schema) : []
+  );
+}
+
+function processInputRule(inputRule, schema) {
+  if (inputRule instanceof Array) {
+    return inputRule.map((rule) => processInputRule(rule, schema));
+  }
+
+  if (inputRule instanceof Function) {
+    inputRule = inputRule({ schema, markInputRule });
+  }
+
+  if (inputRule instanceof InputRule) {
+    return inputRule;
+  }
+
+  if (
+    inputRule.match instanceof RegExp &&
+    inputRule.handler instanceof Function
+  ) {
+    return new InputRule(inputRule.match, inputRule.handler, inputRule.options);
+  }
+
+  throw new Error("Input rule must have a match regex and a handler function");
+}
+
+function orderedListRule(nodeType) {
+  return wrappingInputRule(
+    /^(\d+)\.\s$/,
+    nodeType,
+    (match) => ({ order: +match[1] }),
+    (match, node) => node.childCount + node.attrs.order === +match[1]
+  );
+}
+
+function bulletListRule(nodeType) {
+  return wrappingInputRule(/^\s*([-+*])\s$/, nodeType);
+}
+
+function headingRule(nodeType, maxLevel) {
+  return textblockTypeInputRule(
+    new RegExp("^(#{1," + maxLevel + "})\\s$"),
+    nodeType,
+    (match) => ({ level: match[1].length })
+  );
+}
+
+// https://discuss.prosemirror.net/t/input-rules-for-wrapping-marks/537
+function markInputRule(regexp, markType, getAttrs) {
+  return new InputRule(regexp, (state, match, start, end) => {
+    const attrs = getAttrs instanceof Function ? getAttrs(match) : getAttrs;
+    const tr = state.tr;
+
+    if (state.doc.rangeHasMark(start, end, markType)) {
+      return false;
+    }
+
+    if (match[1]) {
+      let textStart = start + match[0].indexOf(match[1]);
+      let textEnd = textStart + match[1].length;
+      if (textEnd < end) {
+        tr.delete(textEnd, end);
+      }
+      if (textStart > start) {
+        tr.delete(start, textStart);
+      }
+      end = start + match[1].length;
+
+      tr.addMark(start, end, markType.create(attrs));
+      tr.removeStoredMark(markType);
+    } else {
+      tr.delete(start, end);
+      tr.insertText(" ");
+      tr.addMark(start, start + 1, markType.create(attrs));
+      tr.removeStoredMark(markType);
+      tr.insertText(" ");
+
+      tr.setSelection(
+        state.selection.constructor.create(tr.doc, start, start + 1)
+      );
+    }
+
+    return tr;
+  });
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/keymap.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/keymap.js
new file mode 100644
index 00000000000..ff0762b5885
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/keymap.js
@@ -0,0 +1,77 @@
+import {
+  chainCommands,
+  exitCode,
+  selectParentNode,
+  setBlockType,
+} from "prosemirror-commands";
+import { redo, undo } from "prosemirror-history";
+import { undoInputRule } from "prosemirror-inputrules";
+import { splitListItem } from "prosemirror-schema-list";
+
+const isMac =
+  typeof navigator !== "undefined"
+    ? /Mac|iP(hone|[oa]d)/.test(navigator.platform)
+    : false;
+
+export function buildKeymap(
+  extensions,
+  schema,
+  initialKeymap,
+  params,
+  includeDefault = true
+) {
+  const keys = {
+    ...initialKeymap,
+    ...extractKeymap(extensions, params),
+  };
+
+  keys["Mod-z"] = undo;
+  keys["Shift-Mod-z"] = redo;
+  keys["Backspace"] = undoInputRule;
+  if (!isMac) {
+    keys["Mod-y"] = redo;
+  }
+  keys["Escape"] = selectParentNode;
+
+  // The above keys are always included
+  if (!includeDefault) {
+    return keys;
+  }
+
+  keys["Shift-Enter"] = chainCommands(exitCode, (state, dispatch) => {
+    if (dispatch) {
+      dispatch(
+        state.tr
+          .replaceSelectionWith(schema.nodes.hard_break.create())
+          .scrollIntoView()
+      );
+    }
+    return true;
+  });
+
+  keys["Mod-Shift-0"] = setBlockType(schema.nodes.paragraph);
+  keys["Enter"] = splitListItem(schema.nodes.list_item);
+
+  for (let level = 1; level <= 6; level++) {
+    keys["Mod-Shift-" + level] = setBlockType(schema.nodes.heading, { level });
+  }
+
+  keys["Mod-Shift-_"] = (state, dispatch) => {
+    dispatch?.(
+      state.tr
+        .replaceSelectionWith(schema.nodes.horizontal_rule.create())
+        .scrollIntoView()
+    );
+    return true;
+  };
+
+  return keys;
+}
+
+function extractKeymap(extensions, params) {
+  return {
+    ...extensions.map(({ keymap }) => {
+      return keymap instanceof Function ? keymap(params) : keymap;
+    }),
+  };
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/parser.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/parser.js
new file mode 100644
index 00000000000..11549a35ddc
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/parser.js
@@ -0,0 +1,84 @@
+import { defaultMarkdownParser, MarkdownParser } from "prosemirror-markdown";
+import { parse } from "../lib/markdown-it";
+
+// TODO(renato): We need a workaround for this parsing issue:
+//   https://github.com/ProseMirror/prosemirror-markdown/issues/82
+//   a solution may be a markStack in the state ignoring nested marks
+
+export default class Parser {
+  #multipleParseSpecs = {};
+
+  constructor(extensions, includeDefault = true) {
+    this.parseTokens = includeDefault
+      ? {
+          ...defaultMarkdownParser.tokens,
+          bbcode_b: { mark: "strong" },
+          bbcode_i: { mark: "em" },
+        }
+      : {};
+
+    this.postParseTokens = includeDefault
+      ? { softbreak: (state) => state.addNode(state.schema.nodes.hard_break) }
+      : {};
+
+    for (const [key, value] of Object.entries(
+      this.#extractParsers(extensions)
+    )) {
+      // Not a ParseSpec
+      if (typeof value === "function") {
+        this.postParseTokens[key] = value;
+      } else {
+        this.parseTokens[key] = value;
+      }
+    }
+  }
+
+  convert(schema, text) {
+    const parser = new MarkdownParser(schema, { parse }, this.parseTokens);
+
+    // Adding function parse handlers directly
+    Object.assign(parser.tokenHandlers, this.postParseTokens);
+
+    return parser.parse(text);
+  }
+
+  #extractParsers(extensions) {
+    const parsers = {};
+    for (const { parse: parseObj } of extensions) {
+      if (!parseObj) {
+        continue;
+      }
+      for (const [token, parseSpec] of Object.entries(parseObj)) {
+        if (parsers[token] !== undefined) {
+          if (this.#multipleParseSpecs[token] === undefined) {
+            // switch to use multipleParseSpecs
+            this.#multipleParseSpecs[token] = [parsers[token]];
+            parsers[token] = this.#multipleParser(token);
+          }
+          this.#multipleParseSpecs[token].push(parseSpec);
+          continue;
+        }
+        parsers[token] = parseSpec;
+      }
+    }
+    return parsers;
+  }
+
+  #multipleParser(tokenName) {
+    return (state, token, tokens, i) => {
+      const parseSpecs = this.#multipleParseSpecs[tokenName];
+
+      for (const parseSpec of parseSpecs) {
+        if (parseSpec(state, token, tokens, i)) {
+          return;
+        }
+      }
+
+      throw new Error(
+        `No parser processed ${tokenName} token for tag: ${
+          token.tag
+        }, attrs: ${JSON.stringify(token.attrs)}`
+      );
+    };
+  }
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/plugin.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/plugin.js
new file mode 100644
index 00000000000..ede21472af7
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/plugin.js
@@ -0,0 +1,49 @@
+import { Plugin } from "prosemirror-state";
+
+export function extractNodeViews(extensions) {
+  /** @type {Record<string, import('prosemirror-view').NodeViewConstructor>} */
+  const allNodeViews = {};
+  for (const { nodeViews } of extensions) {
+    if (nodeViews) {
+      for (const [name, NodeViewClass] of Object.entries(nodeViews)) {
+        allNodeViews[name] = (...args) => new NodeViewClass(...args);
+      }
+    }
+  }
+  return allNodeViews;
+}
+
+export function extractPlugins(extensions, params, view) {
+  return (
+    extensions
+      .flatMap((extension) => extension.plugins || [])
+      .flatMap((plugin) => processPlugin(plugin, params, view))
+      // filter async plugins from initial load
+      .filter(Boolean)
+  );
+}
+
+function processPlugin(pluginArg, params, handleAsyncPlugin) {
+  if (typeof pluginArg === "function") {
+    const ret = pluginArg(params);
+
+    if (ret instanceof Promise) {
+      ret.then((plugin) => handleAsyncPlugin(processPlugin(plugin, params)));
+      return;
+    }
+
+    return processPlugin(ret, params, handleAsyncPlugin);
+  }
+
+  if (pluginArg instanceof Array) {
+    return pluginArg.map((plugin) =>
+      processPlugin(plugin, params, handleAsyncPlugin)
+    );
+  }
+
+  if (pluginArg instanceof Plugin) {
+    return pluginArg;
+  }
+
+  return new Plugin(pluginArg);
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/schema.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/schema.js
new file mode 100644
index 00000000000..4a11815e773
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/schema.js
@@ -0,0 +1,41 @@
+import OrderedMap from "orderedmap";
+import { schema as defaultMarkdownSchema } from "prosemirror-markdown";
+import { Schema } from "prosemirror-model";
+
+export function createSchema(extensions, includeDefault = true) {
+  let nodes = includeDefault
+    ? defaultMarkdownSchema.spec.nodes
+    : new OrderedMap([]);
+
+  let marks = includeDefault
+    ? defaultMarkdownSchema.spec.marks
+    : new OrderedMap([]);
+
+  for (const [type, spec] of Object.entries(extractNodes(extensions))) {
+    nodes = nodes.update(type, spec);
+  }
+
+  for (const [type, spec] of Object.entries(extractMarks(extensions))) {
+    marks = spec.before
+      ? marks.addBefore(spec.before, type, spec)
+      : marks.update(type, spec);
+  }
+
+  return new Schema({ nodes, marks });
+}
+
+function extractNodes(extensions) {
+  const nodes = {};
+  for (const extension of extensions) {
+    Object.assign(nodes, extension.nodeSpec);
+  }
+  return nodes;
+}
+
+function extractMarks(extensions) {
+  const marks = {};
+  for (const extension of extensions) {
+    Object.assign(marks, extension.markSpec);
+  }
+  return marks;
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/core/serializer.js b/app/assets/javascripts/discourse/app/static/prosemirror/core/serializer.js
new file mode 100644
index 00000000000..224238fbbc3
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/core/serializer.js
@@ -0,0 +1,36 @@
+import {
+  defaultMarkdownSerializer,
+  MarkdownSerializer,
+} from "prosemirror-markdown";
+
+export default class Serializer {
+  #pmSerializer;
+
+  constructor(extensions, includeDefault = true) {
+    this.nodes = includeDefault ? { ...defaultMarkdownSerializer.nodes } : {};
+    this.nodes.hard_break = (state) => state.write("\n");
+
+    this.marks = includeDefault ? { ...defaultMarkdownSerializer.marks } : {};
+
+    this.#extractNodeSerializers(extensions);
+    this.#extractMarkSerializers(extensions);
+
+    this.#pmSerializer = new MarkdownSerializer(this.nodes, this.marks);
+  }
+
+  convert(doc) {
+    return this.#pmSerializer.serialize(doc);
+  }
+
+  #extractNodeSerializers(extensions) {
+    for (const { serializeNode } of extensions) {
+      Object.assign(this.nodes, serializeNode);
+    }
+  }
+
+  #extractMarkSerializers(extensions) {
+    for (const { serializeMark } of extensions) {
+      Object.assign(this.marks, serializeMark);
+    }
+  }
+}
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/extensions/placeholder.js b/app/assets/javascripts/discourse/app/static/prosemirror/extensions/placeholder.js
new file mode 100644
index 00000000000..ac0cdee99a6
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/extensions/placeholder.js
@@ -0,0 +1,56 @@
+/**
+ * This extension is considered a "core" extension, it's autoloaded by ProsemirrorEditor
+ *
+ * @type {RichEditorExtension}
+ */
+const extension = {
+  plugins({
+    pmState: { Plugin },
+    pmView: { Decoration, DecorationSet },
+    getContext,
+  }) {
+    let placeholder;
+
+    return new Plugin({
+      view() {
+        placeholder = getContext().placeholder;
+        return {};
+      },
+      state: {
+        init() {
+          return placeholder;
+        },
+        apply(tr) {
+          const contextChanged = tr.getMeta("discourseContextChanged");
+          if (contextChanged?.key === "placeholder") {
+            placeholder = contextChanged.value;
+          }
+
+          return placeholder;
+        },
+      },
+      props: {
+        decorations(state) {
+          const { $head } = state.selection;
+
+          if (
+            state.doc.childCount === 1 &&
+            state.doc.firstChild === $head.parent &&
+            isEmptyParagraph($head.parent)
+          ) {
+            const decoration = Decoration.node($head.before(), $head.after(), {
+              "data-placeholder": this.getState(state),
+            });
+            return DecorationSet.create(state.doc, [decoration]);
+          }
+        },
+      },
+    });
+  },
+};
+
+function isEmptyParagraph(node) {
+  return node.type.name === "paragraph" && node.nodeSize === 2;
+}
+
+export default extension;
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/extensions/register-default.js b/app/assets/javascripts/discourse/app/static/prosemirror/extensions/register-default.js
new file mode 100644
index 00000000000..886992ce60d
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/extensions/register-default.js
@@ -0,0 +1,11 @@
+import { registerRichEditorExtension } from "discourse/lib/composer/rich-editor-extensions";
+
+/**
+ * List of default extensions
+ * ProsemirrorEditor autoloads them when includeDefault=true (the default)
+ *
+ * @type {RichEditorExtension[]}
+ */
+const defaultExtensions = [];
+
+defaultExtensions.forEach(registerRichEditorExtension);
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/lib/markdown-it.js b/app/assets/javascripts/discourse/app/static/prosemirror/lib/markdown-it.js
new file mode 100644
index 00000000000..e9cc3979172
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/lib/markdown-it.js
@@ -0,0 +1,27 @@
+import { buildEngine } from "discourse/static/markdown-it";
+import loadPluginFeatures from "discourse/static/markdown-it/features";
+import defaultFeatures from "discourse-markdown-it/features/index";
+
+let engine;
+
+function getEngine() {
+  engine ??= buildEngine({
+    featuresOverride: [...defaultFeatures, ...loadPluginFeatures()]
+      .map(({ id }) => id)
+      // Avoid oneboxing when parsing, we'll handle that separately
+      .filter((id) => id !== "onebox"),
+  });
+
+  return engine;
+}
+
+export const parse = (text) => getEngine().parse(text);
+
+export const getLinkify = () => getEngine().linkify;
+
+export const isBoundary = (str, index) =>
+  !str ||
+  getEngine().options.engine.utils.isWhiteSpace(str.charCodeAt(index)) ||
+  getEngine().options.engine.utils.isPunctChar(
+    String.fromCharCode(str.charCodeAt(index))
+  );
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/lib/plugin-utils.js b/app/assets/javascripts/discourse/app/static/prosemirror/lib/plugin-utils.js
new file mode 100644
index 00000000000..050e9102540
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/lib/plugin-utils.js
@@ -0,0 +1 @@
+export { getLinkify, isBoundary } from "../lib/markdown-it";
diff --git a/app/assets/javascripts/discourse/app/static/prosemirror/lib/text-manipulation.js b/app/assets/javascripts/discourse/app/static/prosemirror/lib/text-manipulation.js
new file mode 100644
index 00000000000..09374e23668
--- /dev/null
+++ b/app/assets/javascripts/discourse/app/static/prosemirror/lib/text-manipulation.js
@@ -0,0 +1,490 @@
+// @ts-check
+import { setOwner } from "@ember/owner";
+import { next } from "@ember/runloop";
+import $ from "jquery";
+import { lift, setBlockType, toggleMark, wrapIn } from "prosemirror-commands";
+import { liftListItem, sinkListItem } from "prosemirror-schema-list";
+import { TextSelection } from "prosemirror-state";
+import { bind } from "discourse/lib/decorators";
+import { i18n } from "discourse-i18n";
+
+/**
+ * @typedef {import("discourse/lib/composer/text-manipulation").TextManipulation} TextManipulation
+ * @typedef {import("discourse/lib/composer/text-manipulation").AutocompleteHandler} AutocompleteHandler
+ * @typedef {import("discourse/lib/composer/text-manipulation").PlaceholderHandler} PlaceholderHandler
+ */
+
+/** @implements {TextManipulation} */
+export default class ProsemirrorTextManipulation {
+  allowPreview = false;
+
+  /** @type {import("prosemirror-model").Schema} */
+  schema;
+  /** @type {import("prosemirror-view").EditorView} */
+  view;
+  /** @type {PlaceholderHandler} */
+  placeholder;
+  /** @type {AutocompleteHandler} */
+  autocompleteHandler;
+  convertFromMarkdown;
+  convertToMarkdown;
+
+  constructor(owner, { schema, view, convertFromMarkdown, convertToMarkdown }) {
+    setOwner(this, owner);
+    this.schema = schema;
+    this.view = view;
+    this.convertFromMarkdown = convertFromMarkdown;
+    this.convertToMarkdown = convertToMarkdown;
+
+    this.placeholder = new ProsemirrorPlaceholderHandler({
+      schema,
+      view,
+      convertFromMarkdown,
+    });
+    this.autocompleteHandler = new ProsemirrorAutocompleteHandler({
+      schema,
+      view,
+      convertFromMarkdown,
+    });
+  }
+
+  getSelected() {
+    const start = this.view.state.selection.from;
+    const end = this.view.state.selection.to;
+    const value = this.view.state.doc.textBetween(start, end, " ", " ");
+    return {
+      start,
+      end,
+      pre: "",
+      value,
+      post: "",
+    };
+  }
+
+  focus() {
+    this.view.focus();
+  }
+
+  blurAndFocus() {
+    this.focus();
+  }
+
+  putCursorAtEnd() {
+    this.focus();
+    next(() => (this.view.dom.scrollTop = this.view.dom.scrollHeight));
+  }
+
+  autocomplete(options) {
+    // @ts-ignore
+    $(this.view.dom).autocomplete(
+      options instanceof Object
+        ? { textHandler: this.autocompleteHandler, ...options }
+        : options
+    );
+  }
+
+  applySurroundSelection(head, tail, exampleKey) {
+    this.applySurround(this.getSelected(), head, tail, exampleKey);
+  }
+
+  applySurround(sel, head, tail, exampleKey) {
+    const applySurroundMap = {
+      italic_text: this.schema.marks.em,
+      bold_text: this.schema.marks.strong,
+      code_title: this.schema.marks.code,
+    };
+
+    if (applySurroundMap[exampleKey]) {
+      toggleMark(applySurroundMap[exampleKey])(
+        this.view.state,
+        this.view.dispatch
+      );
+
+      return;
+    }
+
+    const text = head + i18n(`composer.${exampleKey}`) + tail;
+    const doc = this.convertFromMarkdown(text);
+
+    this.view.dispatch(
+      this.view.state.tr.replaceWith(sel.start, sel.end, doc.content.firstChild)
+    );
+  }
+
+  addText(sel, text) {
+    const doc = this.convertFromMarkdown(text);
+
+    // assumes it returns a single block node
+    const content =
+      doc.content.firstChild.type.name === "paragraph"
+        ? doc.content.firstChild.content
+        : doc.content.firstChild;
+
+    this.view.dispatch(
+      this.view.state.tr.replaceWith(sel.start, sel.end, content)
+    );
+
+    this.focus();
+  }
+
+  insertBlock(block) {
+    const doc = this.convertFromMarkdown(block);
+    const node = doc.content.firstChild;
+
+    const tr = this.view.state.tr.replaceSelectionWith(node);
+    if (!tr.selection.$from.nodeAfter) {
+      tr.setSelection(new TextSelection(tr.doc.resolve(tr.selection.from + 1)));
+    }
+    this.view.dispatch(tr);
+
+    this.focus();
+  }
+
+  applyList(_selection, head, exampleKey) {
+    let command;
+
+    const isInside = (type) => {
+      const $from = this.view.state.selection.$from;
+      for (let depth = $from.depth; depth > 0; depth--) {
+        const parent = $from.node(depth);
+        if (parent.type === type) {
+          return true;
+        }
+      }
+      return false;
+    };
+
+    if (exampleKey === "list_item") {
+      const nodeType =
+        head === "* "
+          ? this.schema.nodes.bullet_list
+          : this.schema.nodes.ordered_list;
+
+      command = isInside(this.schema.nodes.list_item) ? lift : wrapIn(nodeType);
+    } else if (exampleKey === "blockquote_text") {
+      command = isInside(this.schema.nodes.blockquote)
+        ? lift
+        : wrapIn(this.schema.nodes.blockquote);
+    } else {
+      throw new Error("Unknown exampleKey");
+    }
+
+    command?.(this.view.state, this.view.dispatch);
+  }
+
+  formatCode() {
+    let command;
+
+    const selection = this.view.state.selection;
+
+    if (selection.$from.parent.type === this.schema.nodes.code_block) {
+      command = setBlockType(this.schema.nodes.paragraph);
+    } else if (
+      selection.$from.pos !== selection.$to.pos &&
+      selection.$from.parent === selection.$to.parent
+    ) {
+      command = toggleMark(this.schema.marks.code);
+    } else {
+      command = setBlockType(this.schema.nodes.code_block);
+    }
+
+    command?.(this.view.state, this.view.dispatch);
+  }
+
+  @bind
+  emojiSelected(code) {
+    this.view.dispatch(
+      this.view.state.tr
+        .replaceSelectionWith(this.schema.nodes.emoji.create({ code }))
+        .insertText(" ")
+    );
+  }
+
+  @bind
+  paste() {
+    // Intentionally no-op
+    // Pasting markdown is being handled by the markdown-paste extension
+    // Pasting a url on top of a text is being handled by the link extension
+  }
+
+  selectText(from, length, opts) {
+    const tr = this.view.state.tr.setSelection(
+      new TextSelection(
+        this.view.state.doc.resolve(from),
+        this.view.state.doc.resolve(from + length)
+      )
+    );
+
+    if (opts.scroll) {
+      tr.scrollIntoView();
+    }
+
+    this.view.dispatch(tr);
+  }
+
+  @bind
+  inCodeBlock() {
+    return this.autocompleteHandler.inCodeBlock();
+  }
+
+  indentSelection(direction) {
+    const { selection } = this.view.state;
+
+    const isInsideListItem =
+      selection.$head.depth > 0 &&
+      selection.$head.node(-1).type === this.schema.nodes.list_item;
+
+    if (isInsideListItem) {
+      const command =
+        direction === "right"
+          ? sinkListItem(this.schema.nodes.list_item)
+          : liftListItem(this.schema.nodes.list_item);
+      command(this.view.state, this.view.dispatch);
+      return true;
+    }
+  }
+
+  insertText(text) {
+    const doc = this.convertFromMarkdown(text);
+
+    this.view.dispatch(
+      this.view.state.tr
+        .replaceSelectionWith(doc.content.firstChild)
+        .scrollIntoView()
+    );
+
+    this.focus();
+  }
+
+  replaceText(oldValue, newValue, opts = {}) {
+    // Replacing Markdown text is not reliable and should eventually be deprecated
+
+    const markdown = this.convertToMarkdown(this.view.state.doc);
+
+    const regex = opts.regex || new RegExp(oldValue, "g");
+    const index = opts.index || 0;
+    let matchCount = 0;
+
+    const newMarkdown = markdown.replace(regex, (match) => {
+      if (matchCount++ === index) {
+        return newValue;
+      }
+      return match;
+    });
+
+    if (markdown === newMarkdown) {
+      return;
+    }
+
+    const newDoc = this.convertFromMarkdown(newMarkdown);
+    if (!newDoc) {
+      return;
+    }
+
+    const diff = newValue.length - oldValue.length;
+    const startOffset = this.view.state.selection.from + diff;
+    const endOffset = this.view.state.selection.to + diff;
+
+    const tr = this.view.state.tr.replaceWith(
+      0,
+      this.view.state.doc.content.size,
+      newDoc.content
+    );
+
+    if (
+      !opts.skipNewSelection &&
+      (opts.forceFocus || this.view.dom === document.activeElement)
+    ) {
+      const adjustedStart = Math.min(startOffset, tr.doc.content.size);
+      const adjustedEnd = Math.min(endOffset, tr.doc.content.size);
+
+      tr.setSelection(TextSelection.create(tr.doc, adjustedStart, adjustedEnd));
+    }
+
+    this.view.dispatch(tr);
+  }
+
+  toggleDirection() {
+    this.view.dom.dir = this.view.dom.dir === "rtl" ? "ltr" : "rtl";
+  }
+}
+
+/** @implements {AutocompleteHandler} */
+class ProsemirrorAutocompleteHandler {
+  /** @type {import("prosemirror-view").EditorView} */
+  view;
+  /** @type {import("prosemirror-model").Schema} */
+  schema;
+  convertFromMarkdown;
+
+  constructor({ schema, view, convertFromMarkdown }) {
+    this.schema = schema;
+    this.view = view;
+    this.convertFromMarkdown = convertFromMarkdown;
+  }
+
+  /**
+   * The textual value of the selected text block
+   * @returns {string}
+   */
+  getValue() {
+    return (
+      (this.view.state.selection.$head.nodeBefore?.textContent ?? "") +
+        (this.view.state.selection.$head.nodeAfter?.textContent ?? "") || " "
+    );
+  }
+
+  /**
+   * Replaces the term between start-end in the currently selected text block
+   *
+   * It uses input rules to convert it to a node if possible
+   *
+   * @param {number} start
+   * @param {number} end
+   * @param {String} term
+   */
+  replaceTerm(start, end, term) {
+    const node = this.view.state.selection.$head.nodeBefore;
+    const from = this.view.state.selection.from - node.nodeSize + start;
+    const to = this.view.state.selection.from - node.nodeSize + end + 1;
+
+    const doc = this.convertFromMarkdown(term);
+
+    const tr = this.view.state.tr.replaceWith(
+      from,
+      to,
+      doc.content.firstChild.content
+    );
+    tr.insertText(" ", tr.selection.from);
+
+    this.view.dispatch(tr);
+  }
+
+  /**
+   * Gets the textual caret position within the selected text block
+   *
+   * @returns {number}
+   */
+  getCaretPosition() {
+    const node = this.view.state.selection.$head.nodeBefore;
+
+    if (!node?.isText) {
+      return 0;
+    }
+
+    return node.nodeSize;
+  }
+
+  getCaretCoords(start) {
+    const node = this.view.state.selection.$head.nodeBefore;
+    const pos = this.view.state.selection.from - node.nodeSize + start;
+    const { left, top } = this.view.coordsAtPos(pos);
+
+    const rootRect = this.view.dom.getBoundingClientRect();
+
+    return {
+      left: left - rootRect.left,
+      top: top - rootRect.top,
+    };
+  }
+
+  async inCodeBlock() {
+    return (
+      this.view.state.selection.$from.parent.type ===
+      this.schema.nodes.code_block
+    );
+  }
+}
+
+/** @implements {PlaceholderHandler} */
+class ProsemirrorPlaceholderHandler {
+  view;
+  schema;
+  convertFromMarkdown;
+
+  constructor({ schema, view, convertFromMarkdown }) {
+    this.schema = schema;
+    this.view = view;
+    this.convertFromMarkdown = convertFromMarkdown;
+  }
+
+  insert(file) {
+    const isEmptyParagraph =
+      this.view.state.selection.$from.parent.type.name === "paragraph" &&
+      this.view.state.selection.$from.parent.nodeSize === 2;
+
+    const imageNode = this.schema.nodes.image.create({
+      src: URL.createObjectURL(file.data),
+      alt: i18n("uploading_filename", { filename: file.name }),
+      title: file.id,
+      width: 120,
+      "data-placeholder": true,
+    });
+
+    this.view.dispatch(
+      this.view.state.tr.insert(
+        this.view.state.selection.from,
+        isEmptyParagraph
+          ? imageNode
+          : this.schema.nodes.paragraph.create(null, imageNode)
+      )
+    );
+  }
+
+  progress() {}
+  progressComplete() {}
+
+  cancelAll() {
+    this.view.state.doc.descendants((node, pos) => {
+      if (
+        node.type === this.schema.nodes.image &&
+        node.attrs["data-placeholder"]
+      ) {
+        this.view.dispatch(this.view.state.tr.delete(pos, pos + node.nodeSize));
+      }
+    });
+  }
+
+  cancel(file) {
+    this.view.state.doc.descendants((node, pos) => {
+      if (
+        node.type === this.schema.nodes.image &&
+        node.attrs["data-placeholder"] &&
+        node.attrs?.title === file.id
+      ) {
+        this.view.dispatch(this.view.state.tr.delete(pos, pos + node.nodeSize));
+      }
+    });
+  }
+
+  success(file, markdown) {
+    /** @type {null | { node: import("prosemirror-model").Node, pos: number }} */
+    let nodeToReplace = null;
+    this.view.state.doc.descendants((node, pos) => {
+      if (
+        node.type === this.schema.nodes.image &&
+        node.attrs["data-placeholder"] &&
+        node.attrs?.title === file.id
+      ) {
+        nodeToReplace = { node, pos };
+        return false;
+      }
+      return true;
+    });
+
+    if (!nodeToReplace) {
+      return;
+    }
+
+    // keeping compatibility with plugins that change the upload markdown
+    const doc = this.convertFromMarkdown(markdown);
+
+    this.view.dispatch(
+      this.view.state.tr.replaceWith(
+        nodeToReplace.pos,
+        nodeToReplace.pos + nodeToReplace.node.nodeSize,
+        doc.content.firstChild.content
+      )
+    );
+  }
+}
diff --git a/app/assets/javascripts/discourse/package.json b/app/assets/javascripts/discourse/package.json
index db0ebf0cbdc..1adf1cf0aff 100644
--- a/app/assets/javascripts/discourse/package.json
+++ b/app/assets/javascripts/discourse/package.json
@@ -34,7 +34,21 @@
     "immer": "^10.1.1",
     "jspreadsheet-ce": "^4.15.0",
     "morphlex": "^0.0.16",
-    "pretty-text": "workspace:1.0.0"
+    "orderedmap": "^2.1.1",
+    "pretty-text": "workspace:1.0.0",
+    "prosemirror-commands": "^1.6.0",
+    "prosemirror-dropcursor": "^1.8.1",
+    "prosemirror-gapcursor": "^1.3.2",
+    "prosemirror-highlightjs": "^0.9.1",
+    "prosemirror-history": "^1.4.1",
+    "prosemirror-inputrules": "^1.4.0",
+    "prosemirror-keymap": "^1.2.2",
+    "prosemirror-markdown": "^1.13.1",
+    "prosemirror-model": "^1.23.0",
+    "prosemirror-schema-list": "^1.4.1",
+    "prosemirror-state": "^1.4.3",
+    "prosemirror-transform": "^1.10.2",
+    "prosemirror-view": "^1.34.3"
   },
   "devDependencies": {
     "@babel/core": "^7.26.7",
diff --git a/app/assets/javascripts/discourse/tests/helpers/rich-editor-helper.gjs b/app/assets/javascripts/discourse/tests/helpers/rich-editor-helper.gjs
new file mode 100644
index 00000000000..53a6284d008
--- /dev/null
+++ b/app/assets/javascripts/discourse/tests/helpers/rich-editor-helper.gjs
@@ -0,0 +1,64 @@
+import { tracked } from "@glimmer/tracking";
+import { click, render, settled, waitFor } from "@ember/test-helpers";
+import DEditor from "discourse/components/d-editor";
+
+export async function testMarkdown(
+  assert,
+  markdown,
+  expectedHtml,
+  expectedMarkdown
+) {
+  const self = new (class {
+    @tracked value = markdown;
+    @tracked view;
+  })();
+  const handleSetup = (textManipulation) => {
+    self.view = textManipulation.view;
+  };
+
+  await render(<template>
+    <DEditor
+      @value={{self.value}}
+      @processPreview={{false}}
+      @onSetup={{handleSetup}}
+    />
+  </template>);
+  await click(".composer-toggle-switch");
+
+  await waitFor(".ProseMirror");
+  await settled();
+  const editor = document.querySelector(".ProseMirror");
+
+  // typeIn for contentEditable isn't reliable, and is slower
+  const tr = self.view.state.tr;
+  // insert a paragraph to enforce serialization
+  tr.insert(
+    tr.doc.content.size,
+    self.view.state.schema.node(
+      "paragraph",
+      null,
+      self.view.state.schema.text("X")
+    )
+  );
+  // then delete it
+  tr.delete(tr.doc.content.size - 3, tr.doc.content.size);
+
+  self.view.dispatch(tr);
+
+  await settled();
+
+  const html = editor.innerHTML
+    // we don't care about some PM-specifics
+    .replace(' class="ProseMirror-selectednode"', "")
+    .replace('<img class="ProseMirror-separator" alt="">', "")
+    .replace('<br class="ProseMirror-trailingBreak">', "")
+    // or artifacts
+    .replace('class=""', "");
+
+  assert.strictEqual(html, expectedHtml, `HTML should match for "${markdown}"`);
+  assert.strictEqual(
+    self.value,
+    expectedMarkdown,
+    `Markdown should match for "${markdown}"`
+  );
+}
diff --git a/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-editor-test.gjs b/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-editor-test.gjs
new file mode 100644
index 00000000000..066b9feec93
--- /dev/null
+++ b/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-editor-test.gjs
@@ -0,0 +1,203 @@
+import { render } from "@ember/test-helpers";
+import { module, test } from "qunit";
+import { resetRichEditorExtensions } from "discourse/lib/composer/rich-editor-extensions";
+import { withPluginApi } from "discourse/lib/plugin-api";
+import ProsemirrorEditor from "discourse/static/prosemirror/components/prosemirror-editor";
+import { setupRenderingTest } from "discourse/tests/helpers/component-test";
+import { testMarkdown } from "discourse/tests/helpers/rich-editor-helper";
+
+module("Integration | Component | prosemirror-editor", function (hooks) {
+  setupRenderingTest(hooks);
+
+  hooks.afterEach(function () {
+    resetRichEditorExtensions();
+  });
+
+  test("renders the editor", async function (assert) {
+    await render(<template><ProsemirrorEditor /></template>);
+    assert.dom(".ProseMirror").exists("it renders the ProseMirror editor");
+  });
+
+  test("renders the editor with minimum extensions", async function (assert) {
+    const minimumExtensions = [
+      { nodeSpec: { doc: { content: "inline*" }, text: { group: "inline" } } },
+    ];
+
+    await render(<template>
+      <ProsemirrorEditor
+        @includeDefault={{false}}
+        @extensions={{minimumExtensions}}
+      />
+    </template>);
+
+    assert.dom(".ProseMirror").exists("it renders the ProseMirror editor");
+  });
+
+  test("supports registered nodeSpec/parser/serializer", async function (assert) {
+    this.siteSettings.rich_editor = true;
+
+    withPluginApi("2.1.0", (api) => {
+      // Multiple parsers can be registered for the same node type
+      api.registerRichEditorExtension({
+        parse: { wrap_open() {}, wrap_close() {} },
+      });
+
+      api.registerRichEditorExtension({
+        nodeSpec: {
+          marquee: {
+            content: "block*",
+            group: "block",
+            parseDOM: [{ tag: "marquee" }],
+            toDOM: () => ["marquee", 0],
+          },
+        },
+        parse: {
+          wrap_open(state, token) {
+            if (token.attrGet("data-wrap") === "marquee") {
+              state.openNode(state.schema.nodes.marquee);
+              return true;
+            }
+          },
+          wrap_close(state) {
+            if (state.top().type.name === "marquee") {
+              state.closeNode();
+              return true;
+            }
+          },
+        },
+        serializeNode: {
+          marquee(state, node) {
+            state.write("[wrap=marquee]\n");
+            state.renderContent(node);
+            state.write("[/wrap]\n\n");
+          },
+        },
+      });
+
+      api.registerRichEditorExtension({
+        parse: { wrap_open() {}, wrap_close() {} },
+      });
+    });
+
+    await testMarkdown(
+      assert,
+      "[wrap=marquee]\nHello\n[wrap=marquee]\nWorld\n[/wrap]\nInner\n[/wrap]\n\nText",
+      "<marquee><p>Hello</p><marquee><p>World</p></marquee><p>Inner</p></marquee><p>Text</p>",
+      "[wrap=marquee]\nHello\n\n[wrap=marquee]\nWorld\n\n[/wrap]\n\nInner\n\n[/wrap]\n\nText"
+    );
+  });
+
+  test("supports registered markSpec/parser/serializer", async function (assert) {
+    this.siteSettings.rich_editor = true;
+
+    withPluginApi("2.1.0", (api) => {
+      api.registerRichEditorExtension({
+        // just for testing purpose - our actual hashtag is a node, not a mark
+        markSpec: {
+          hashtag: {
+            parseDOM: [{ tag: "span.hashtag-raw" }],
+            toDOM: () => ["span", { class: "hashtag-raw" }],
+          },
+        },
+        parse: {
+          span_open(state, token, tokens, i) {
+            if (token.attrGet("class") === "hashtag-raw") {
+              // Remove the # from the content
+              tokens[i + 1].content = tokens[i + 1].content.slice(1);
+              state.openMark(state.schema.marks.hashtag.create());
+              return true;
+            }
+          },
+          span_close(state) {
+            state.closeMark(state.schema.marks.hashtag);
+          },
+        },
+        serializeMark: { hashtag: { open: "#", close: "" } },
+      });
+    });
+
+    await testMarkdown(
+      assert,
+      "Hello #tag #test",
+      '<p>Hello <span class="hashtag-raw">tag</span> <span class="hashtag-raw">test</span></p>',
+      "Hello #tag #test"
+    );
+  });
+
+  test("supports registered nodeViews", async function (assert) {
+    this.siteSettings.rich_editor = true;
+
+    const state = {};
+
+    withPluginApi("2.1.0", (api) => {
+      api.registerRichEditorExtension({
+        nodeViews: {
+          paragraph: class CustomNodeView {
+            constructor() {
+              this.dom = document.createElement("p");
+              this.dom.className = "custom-p";
+
+              state.updated = true;
+            }
+          },
+        },
+      });
+    });
+
+    await render(<template><ProsemirrorEditor /></template>);
+
+    assert.true(
+      state.updated,
+      "it calls the update method of the custom node view"
+    );
+
+    assert.dom(".custom-p").exists("it renders the custom node view for p");
+  });
+
+  test("supports registered plugins with array, object or function", async function (assert) {
+    this.siteSettings.rich_editor = true;
+
+    const state = {};
+
+    withPluginApi("2.1.0", (api) => {
+      // plugins can be an array
+      api.registerRichEditorExtension({
+        plugins: [
+          {
+            view() {
+              state.plugin1 = true;
+              return {};
+            },
+          },
+        ],
+      });
+
+      // or the plugin object itself
+      api.registerRichEditorExtension({
+        plugins: {
+          view() {
+            state.plugin2 = true;
+            return {};
+          },
+        },
+      });
+
+      // or a function that returns the plugin object
+      api.registerRichEditorExtension({
+        plugins: ({ pmState: { Plugin } }) =>
+          new Plugin({
+            view() {
+              state.plugin3 = true;
+              return {};
+            },
+          }),
+      });
+    });
+
+    await render(<template><ProsemirrorEditor /></template>);
+
+    assert.true(state.plugin1, "plugin1's view fn was called");
+    assert.true(state.plugin2, "plugin2's view fn was called");
+    assert.true(state.plugin3, "plugin3's view fn was called");
+  });
+});
diff --git a/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-markdown-test.gjs b/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-markdown-test.gjs
new file mode 100644
index 00000000000..eeb54849e21
--- /dev/null
+++ b/app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/prosemirror-markdown-test.gjs
@@ -0,0 +1,152 @@
+import { module, test } from "qunit";
+import { setupRenderingTest } from "discourse/tests/helpers/component-test";
+import { testMarkdown } from "discourse/tests/helpers/rich-editor-helper";
+
+module(
+  "Integration | Component | prosemirror-editor - prosemirror-markdown defaults",
+  function (hooks) {
+    setupRenderingTest(hooks);
+
+    const testCases = {
+      "paragraphs and hard breaks": [
+        ["Hello", "<p>Hello</p>", "Hello"],
+        ["Hello\nWorld", "<p>Hello<br>World</p>", "Hello\nWorld"],
+        ["Hello\n\nWorld", "<p>Hello</p><p>World</p>", "Hello\n\nWorld"],
+      ],
+      blockquotes: [
+        ["> Hello", "<blockquote><p>Hello</p></blockquote>", "> Hello"],
+        [
+          "> Hello\n> World",
+          "<blockquote><p>Hello<br>World</p></blockquote>",
+          "> Hello\n> World",
+        ],
+        [
+          "> Hello\n\n> World",
+          "<blockquote><p>Hello</p></blockquote><blockquote><p>World</p></blockquote>",
+          "> Hello\n\n> World",
+        ],
+      ],
+      "horizontal rule": [
+        [
+          "Hey\n\n---",
+          '<p>Hey</p><div contenteditable="false" draggable="true"><hr></div>',
+          "Hey\n\n---",
+        ],
+        [
+          "***",
+          '<div contenteditable="false" draggable="true"><hr></div>',
+          "---",
+        ],
+      ],
+      "heading (level 1-6)": [
+        ["# Hello", "<h1>Hello</h1>", "# Hello"],
+        ["# Hello\nWorld", "<h1>Hello</h1><p>World</p>", "# Hello\n\nWorld"],
+        ["## Hello", "<h2>Hello</h2>", "## Hello"],
+        ["### Hello", "<h3>Hello</h3>", "### Hello"],
+        ["#### Hello", "<h4>Hello</h4>", "#### Hello"],
+        ["##### Hello", "<h5>Hello</h5>", "##### Hello"],
+        ["###### Hello", "<h6>Hello</h6>", "###### Hello"],
+      ],
+      "code block": [
+        ["```\nHello\n```", "<pre><code>Hello</code></pre>", "```\nHello\n```"],
+        [
+          "```\nHello\nWorld\n```",
+          "<pre><code>Hello\nWorld</code></pre>",
+          "```\nHello\nWorld\n```",
+        ],
+        [
+          "```\nHello\n\nWorld\n```",
+          "<pre><code>Hello\n\nWorld</code></pre>",
+          "```\nHello\n\nWorld\n```",
+        ],
+        [
+          "```ruby\nHello\n```\n\nWorld",
+          '<pre data-params="ruby"><code>Hello</code></pre><p>World</p>',
+          "```ruby\nHello\n```\n\nWorld",
+        ],
+      ],
+      "ordered lists": [
+        [
+          "1. Hello",
+          `<ol data-tight="true"><li><p>Hello</p></li></ol>`,
+          "1. Hello",
+        ],
+        [
+          "1. Hello\n2. World",
+          `<ol data-tight="true"><li><p>Hello</p></li><li><p>World</p></li></ol>`,
+          "1. Hello\n2. World",
+        ],
+        [
+          "5. Hello\n\n6. World",
+          `<ol start="5"><li><p>Hello</p></li><li><p>World</p></li></ol>`,
+          "5. Hello\n\n6. World",
+        ],
+      ],
+      "bullet lists": [
+        [
+          "* Hello",
+          '<ul data-tight="true"><li><p>Hello</p></li></ul>',
+          "* Hello",
+        ],
+        [
+          "* Hello\n* World",
+          '<ul data-tight="true"><li><p>Hello</p></li><li><p>World</p></li></ul>',
+          "* Hello\n* World",
+        ],
+        [
+          "* Hello\n\n* World",
+          "<ul><li><p>Hello</p></li><li><p>World</p></li></ul>",
+          "* Hello\n\n* World",
+        ],
+      ],
+      images: [
+        [
+          "![alt](src)",
+          '<p><img src="src" alt="alt" contenteditable="false" draggable="true"></p>',
+          "![alt](src)",
+        ],
+        [
+          '![alt](src "title")',
+          '<p><img src="src" alt="alt" title="title" contenteditable="false" draggable="true"></p>',
+          '![alt](src "title")',
+        ],
+      ],
+      em: [
+        ["*Hello*", "<p><em>Hello</em></p>", "*Hello*"],
+        ["_Hello_", "<p><em>Hello</em></p>", "*Hello*"],
+      ],
+      strong: [
+        ["**Hello**", "<p><strong>Hello</strong></p>", "**Hello**"],
+        ["__Hello__", "<p><strong>Hello</strong></p>", "**Hello**"],
+      ],
+      link: [
+        ["[text](href)", '<p><a href="href">text</a></p>', "[text](href)"],
+        [
+          '[text](href "title")',
+          '<p><a href="href" title="title">text</a></p>',
+          '[text](href "title")',
+        ],
+      ],
+      code: [
+        ["Hel`lo wo`rld", "<p>Hel<code>lo wo</code>rld</p>", "Hel`lo wo`rld"],
+      ],
+      "all marks": [
+        [
+          "___[`Hello`](https://example.com)___",
+          '<p><em><strong><a href="https://example.com"><code>Hello</code></a></strong></em></p>',
+          "***[`Hello`](https://example.com)***",
+        ],
+      ],
+    };
+
+    Object.entries(testCases).forEach(([name, tests]) => {
+      tests.forEach(([markdown, expectedHtml, expectedMarkdown]) => {
+        test(name, async function (assert) {
+          this.siteSettings.rich_editor = true;
+
+          await testMarkdown(assert, markdown, expectedHtml, expectedMarkdown);
+        });
+      });
+    });
+  }
+);
diff --git a/app/assets/stylesheets/common.scss b/app/assets/stylesheets/common.scss
index 57e76d81116..1ae638a0fac 100644
--- a/app/assets/stylesheets/common.scss
+++ b/app/assets/stylesheets/common.scss
@@ -18,6 +18,7 @@
 @import "common/topic-timeline";
 @import "common/loading-slider";
 @import "common/float-kit/_index";
+@import "common/rich-editor";
 @import "common/login/_index";
 @import "common/table-builder/_index";
 @import "common/post-action-feedback";
diff --git a/app/assets/stylesheets/common/components/_index.scss b/app/assets/stylesheets/common/components/_index.scss
index b91497b3689..9c7b732253b 100644
--- a/app/assets/stylesheets/common/components/_index.scss
+++ b/app/assets/stylesheets/common/components/_index.scss
@@ -12,6 +12,7 @@
 @import "char-counter";
 @import "conditional-loading-section";
 @import "calendar-date-time-input";
+@import "composer-toggle-switch";
 @import "convert-to-public-topic-modal";
 @import "d-toggle-switch";
 @import "date-input";
diff --git a/app/assets/stylesheets/common/components/composer-toggle-switch.scss b/app/assets/stylesheets/common/components/composer-toggle-switch.scss
new file mode 100644
index 00000000000..c5442143181
--- /dev/null
+++ b/app/assets/stylesheets/common/components/composer-toggle-switch.scss
@@ -0,0 +1,93 @@
+.composer-toggle-switch {
+  --toggle-switch-width: 40px;
+  --toggle-switch-height: 24px;
+  height: 100%;
+  grid-column: span 2;
+  justify-content: center;
+  display: flex;
+  align-items: center;
+  border: 0;
+  padding: 0;
+  background: transparent;
+
+  &:focus-visible {
+    outline: none;
+  }
+
+  &[disabled] {
+    opacity: 0.5;
+    cursor: not-allowed;
+  }
+
+  &__slider {
+    display: inline-block;
+    background: var(--primary-low);
+    width: var(--toggle-switch-width);
+    height: var(--toggle-switch-height);
+    position: relative;
+    vertical-align: middle;
+    border-radius: 0.25em;
+
+    :focus-visible & {
+      outline: 2px solid var(--tertiary);
+      outline-offset: 2px;
+    }
+
+    &::before {
+      content: "";
+      display: block;
+      position: absolute;
+      background-color: var(--tertiary-low);
+      width: calc(var(--toggle-switch-height) - 2px);
+      height: calc(var(--toggle-switch-height) - 4px);
+      top: 2px;
+      transition: left 0.25s, right 0.25s;
+      border-radius: 0.25em;
+      box-shadow: 0 1px 3px 1px rgba(0, 0, 0, 0.1);
+
+      .--markdown & {
+        left: 2px;
+      }
+
+      .--rte & {
+        right: 2px;
+      }
+
+      @media (prefers-reduced-motion: reduce) {
+        transition-duration: 0ms;
+      }
+    }
+  }
+
+  &__left-icon,
+  &__right-icon {
+    display: inline-block;
+    position: absolute;
+    opacity: 0;
+    transition: opacity 0.25s left 0.25s, right 0.25s;
+    height: 100%;
+    width: calc(var(--toggle-switch-height) - 2px);
+
+    @media (prefers-reduced-motion: reduce) {
+      transition-duration: 0ms;
+    }
+
+    .--markdown & {
+      left: 2px;
+    }
+
+    .--rte & {
+      right: 2px;
+    }
+
+    &.--active {
+      opacity: 1;
+    }
+
+    .d-icon {
+      font-size: var(--font-down-1);
+      color: var(--primary);
+      vertical-align: text-bottom;
+    }
+  }
+}
diff --git a/app/assets/stylesheets/common/rich-editor/_index.scss b/app/assets/stylesheets/common/rich-editor/_index.scss
new file mode 100644
index 00000000000..31b532f02a9
--- /dev/null
+++ b/app/assets/stylesheets/common/rich-editor/_index.scss
@@ -0,0 +1 @@
+@import "rich-editor";
diff --git a/app/assets/stylesheets/common/rich-editor/rich-editor.scss b/app/assets/stylesheets/common/rich-editor/rich-editor.scss
new file mode 100644
index 00000000000..0a9dd7b5df9
--- /dev/null
+++ b/app/assets/stylesheets/common/rich-editor/rich-editor.scss
@@ -0,0 +1,256 @@
+.ProseMirror-container {
+  margin: 0;
+  overscroll-behavior: contain;
+  overflow-anchor: none;
+  flex-direction: column;
+  overflow-y: auto;
+  overflow-x: hidden;
+  display: flex;
+  height: 100%;
+}
+
+.ProseMirror {
+  outline: 0;
+  padding: 0 0.625rem;
+
+  > div:first-child,
+  > details:first-child {
+    // This is hacky, but helps having the leading gapcursor at the right position
+    &.ProseMirror-gapcursor {
+      position: relative;
+      display: block;
+    }
+    margin-top: 0.5rem;
+  }
+
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6 {
+    margin: 30px 0 10px;
+
+    &:first-child {
+      margin-top: 10px;
+    }
+  }
+
+  h1 {
+    font-size: var(--font-up-3-rem);
+  }
+
+  h2 {
+    font-size: var(--font-up-2-rem);
+  }
+
+  h3 {
+    font-size: var(--font-up-1-rem);
+  }
+
+  img {
+    display: inline-block;
+    height: auto;
+    max-width: 100%;
+
+    &[data-placeholder="true"] {
+      animation: placeholder 1.5s infinite;
+
+      @keyframes placeholder {
+        0% {
+          opacity: 0.6;
+        }
+
+        50% {
+          opacity: 0.4;
+        }
+
+        100% {
+          opacity: 0.6;
+        }
+      }
+    }
+  }
+
+  ul,
+  ol {
+    padding-left: 1.25em;
+
+    &[data-tight="true"] > li > p {
+      margin-top: 0;
+      margin-bottom: 0;
+    }
+  }
+
+  p {
+    line-height: 1.5;
+
+    &:first-child {
+      margin-top: 0.59rem;
+    }
+  }
+
+  p[data-placeholder]::before {
+    pointer-events: none;
+    position: absolute;
+    padding-top: 2px;
+    padding-right: 0.5rem;
+    content: attr(data-placeholder);
+    color: var(--primary-400);
+    line-height: 1.1;
+  }
+
+  del {
+    background-color: var(--danger-low);
+  }
+
+  ins {
+    background-color: var(--success-low);
+  }
+
+  mark {
+    background-color: var(--highlight);
+  }
+
+  td {
+    padding: 3px 3px 3px 0.5em;
+  }
+
+  th {
+    padding-bottom: 2px;
+    font-weight: bold;
+    color: var(--primary);
+  }
+
+  kbd {
+    // I believe this shouldn't be `inline-flex` in posts either (test with emojis before/after text to see why),
+    // but overriding just for the editor for now
+    display: inline;
+    padding-top: 0.2rem;
+  }
+
+  .onebox-wrapper {
+    white-space: normal;
+  }
+
+  .code-block {
+    position: relative;
+  }
+
+  .code-language-select {
+    position: absolute;
+    right: 0.25rem;
+    top: -0.6rem;
+    border: 1px solid var(--primary-low);
+    border-radius: var(--d-border-radius);
+    background-color: var(--primary-very-low);
+    color: var(--primary-medium);
+    font-size: var(--font-down-1-rem);
+  }
+
+  .html-block {
+    position: relative;
+    border: 1px dashed var(--primary-low-mid);
+
+    &::after {
+      position: absolute;
+      right: 0;
+      top: 0;
+      content: "HTML";
+      font-size: var(--font-down-2-rem);
+      color: var(--primary-low-mid);
+      z-index: 1;
+    }
+  }
+}
+
+/*********************************************************
+ Section below from prosemirror-view/style/prosemirror.css
+ ********************************************************/
+
+.ProseMirror {
+  position: relative;
+}
+
+.ProseMirror {
+  word-wrap: break-word;
+  white-space: break-spaces;
+}
+
+.ProseMirror pre {
+  white-space: pre-wrap;
+}
+
+.ProseMirror li {
+  position: relative;
+}
+
+.ProseMirror-hideselection *::selection {
+  background: transparent;
+}
+
+.ProseMirror-hideselection {
+  caret-color: transparent;
+}
+
+/* See https://github.com/ProseMirror/prosemirror/issues/1421#issuecomment-1759320191 */
+.ProseMirror [draggable][contenteditable="false"] {
+  user-select: text;
+}
+
+.ProseMirror-selectednode {
+  outline: 2px solid #8cf;
+}
+
+/* Make sure li selections wrap around markers */
+li.ProseMirror-selectednode {
+  outline: none;
+}
+
+li.ProseMirror-selectednode::after {
+  content: "";
+  position: absolute;
+  left: -32px;
+  right: -2px;
+  top: -2px;
+  bottom: -2px;
+  border: 2px solid #8cf;
+  pointer-events: none;
+}
+
+/* Protect against generic img rules */
+.ProseMirror-separator {
+  display: inline !important;
+  border: none !important;
+  margin: 0 !important;
+}
+
+/************************************************************
+ Section below from prosemirror-gapcursor/style/gapcursor.css
+ ***********************************************************/
+
+.ProseMirror-gapcursor {
+  display: none;
+  pointer-events: none;
+  position: absolute;
+}
+
+.ProseMirror-gapcursor::after {
+  content: "";
+  display: block;
+  position: absolute;
+  top: -2px;
+  width: 20px;
+  border-top: 1px solid var(--primary);
+  animation: ProseMirror-cursor-blink 1.1s steps(2, start) infinite;
+}
+
+@keyframes ProseMirror-cursor-blink {
+  to {
+    visibility: hidden;
+  }
+}
+
+.ProseMirror-focused .ProseMirror-gapcursor {
+  display: block;
+}
diff --git a/app/assets/stylesheets/mobile/compose.scss b/app/assets/stylesheets/mobile/compose.scss
index df7c74f675c..fafa19e08a1 100644
--- a/app/assets/stylesheets/mobile/compose.scss
+++ b/app/assets/stylesheets/mobile/compose.scss
@@ -11,6 +11,7 @@
     padding: 6px;
     padding-bottom: unquote("max(env(safe-area-inset-bottom), 6px)");
     flex-grow: 1;
+    min-height: 0;
   }
 
   &.open {
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 3df2e7b5658..c2fcb18c7e4 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -3554,3 +3554,7 @@ experimental:
   use_overhauled_theme_color_palette:
     default: false
     hidden: true
+  rich_editor:
+    client: true
+    default: false
+    hidden: true
diff --git a/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
index b007e2fdbc4..0721666139b 100644
--- a/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
+++ b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
@@ -7,6 +7,10 @@ in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.1.0] - 2024-01-29
+
+- Added `registerRichEditorExtension` which allows plugins/TCs to register an extension for the rich text editor.
+
 ## [2.0.1] - 2025-01-29
 
 - Added `registerReportModeComponent`. This allows plugins to register different report display modes in addition to the built-in core ones like `chart`, `table`, and so on defined in `Report::MODES`.
diff --git a/jsconfig.json b/jsconfig.json
index 16c041a63cb..6868dd117f5 100644
--- a/jsconfig.json
+++ b/jsconfig.json
@@ -5,6 +5,7 @@
     "module": "esnext",
     "moduleResolution": "bundler",
     "experimentalDecorators": true,
+    "allowJs": true,
     "paths": {
       "discourse/*": [
         "./app/assets/javascripts/discourse/app/*"
diff --git a/lib/svg_sprite.rb b/lib/svg_sprite.rb
index 5f8e9c6ae7a..95adf349023 100644
--- a/lib/svg_sprite.rb
+++ b/lib/svg_sprite.rb
@@ -4,6 +4,7 @@ module SvgSprite
   SVG_ICONS =
     Set.new(
       %w[
+        a
         address-book
         align-left
         anchor
@@ -106,6 +107,7 @@ module SvgSprite
         fab-instagram
         fab-linkedin-in
         fab-linux
+        fab-markdown
         fab-threads
         fab-threads-square
         fab-twitter
diff --git a/plugins/chat/assets/javascripts/discourse/components/chat-channel.gjs b/plugins/chat/assets/javascripts/discourse/components/chat-channel.gjs
index 4077e9a7280..0189274ebba 100644
--- a/plugins/chat/assets/javascripts/discourse/components/chat-channel.gjs
+++ b/plugins/chat/assets/javascripts/discourse/components/chat-channel.gjs
@@ -658,7 +658,11 @@ export default class ChatChannel extends Component {
       return;
     }
 
-    if (!target || /^(INPUT|TEXTAREA|SELECT)$/.test(target.tagName)) {
+    if (
+      !target ||
+      /^(INPUT|TEXTAREA|SELECT)$/.test(target.tagName) ||
+      target.closest('[contenteditable="true"]')
+    ) {
       return;
     }
 
diff --git a/plugins/chat/assets/javascripts/discourse/initializers/chat-keyboard-shortcuts.js b/plugins/chat/assets/javascripts/discourse/initializers/chat-keyboard-shortcuts.js
index 6b5bda472ce..427304c2d2d 100644
--- a/plugins/chat/assets/javascripts/discourse/initializers/chat-keyboard-shortcuts.js
+++ b/plugins/chat/assets/javascripts/discourse/initializers/chat-keyboard-shortcuts.js
@@ -58,10 +58,10 @@ export default {
       const inputs = ["input", "textarea", "select", "button"];
       const elementTagName = el?.tagName.toLowerCase();
 
-      if (inputs.includes(elementTagName)) {
-        return false;
-      }
-      return true;
+      return (
+        inputs.includes(elementTagName) ||
+        !!el?.closest('[contenteditable="true"]')
+      );
     };
     const modifyComposerSelection = (event, type) => {
       if (!isChatComposer(event.target)) {
@@ -87,7 +87,7 @@ export default {
     };
 
     const openChatDrawer = (event) => {
-      if (!isInputSelection(event.target)) {
+      if (isInputSelection(event.target)) {
         return;
       }
       event.preventDefault();
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index a42a70d275f..86348441749 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -329,9 +329,51 @@ importers:
       morphlex:
         specifier: ^0.0.16
         version: 0.0.16
+      orderedmap:
+        specifier: ^2.1.1
+        version: 2.1.1
       pretty-text:
         specifier: workspace:1.0.0
         version: link:../pretty-text
+      prosemirror-commands:
+        specifier: ^1.6.0
+        version: 1.6.2
+      prosemirror-dropcursor:
+        specifier: ^1.8.1
+        version: 1.8.1
+      prosemirror-gapcursor:
+        specifier: ^1.3.2
+        version: 1.3.2
+      prosemirror-highlightjs:
+        specifier: ^0.9.1
+        version: 0.9.1(highlight.js@11.11.1)(prosemirror-model@1.24.1)(prosemirror-state@1.4.3)(prosemirror-view@1.37.1)
+      prosemirror-history:
+        specifier: ^1.4.1
+        version: 1.4.1
+      prosemirror-inputrules:
+        specifier: ^1.4.0
+        version: 1.4.0
+      prosemirror-keymap:
+        specifier: ^1.2.2
+        version: 1.2.2
+      prosemirror-markdown:
+        specifier: ^1.13.1
+        version: 1.13.1
+      prosemirror-model:
+        specifier: ^1.23.0
+        version: 1.24.1
+      prosemirror-schema-list:
+        specifier: ^1.4.1
+        version: 1.5.0
+      prosemirror-state:
+        specifier: ^1.4.3
+        version: 1.4.3
+      prosemirror-transform:
+        specifier: ^1.10.2
+        version: 1.10.2
+      prosemirror-view:
+        specifier: ^1.34.3
+        version: 1.37.1
     devDependencies:
       '@babel/core':
         specifier: ^7.26.7
@@ -6642,6 +6684,9 @@ packages:
   ordered-read-streams@1.0.1:
     resolution: {integrity: sha512-Z87aSjx3r5c0ZB7bcJqIgIRX5bxR7A4aSzvIbaxd0oTkWBCOoKfuGHiKj60CHVUgg1Phm5yMZzBdt8XqRs73Mw==}
 
+  orderedmap@2.1.1:
+    resolution: {integrity: sha512-TvAWxi0nDe1j/rtMcWcIj94+Ffe6n7zhow33h40SKxmsmozs6dz/e+EajymfoFcHd7sxNn8yHM8839uixMOV6g==}
+
   os-locale@5.0.0:
     resolution: {integrity: sha512-tqZcNEDAIZKBEPnHPlVDvKrp7NzgLi7jRmhKiUoa2NUmhl13FtkAGLUVR+ZsYvApBQdBfYm43A4tXXQ4IrYLBA==}
     engines: {node: '>=10'}
@@ -7021,6 +7066,50 @@ packages:
   proper-lockfile@4.1.2:
     resolution: {integrity: sha512-TjNPblN4BwAWMXU8s9AEz4JmQxnD1NNL7bNOY/AKUzyamc379FWASUhc/K1pL2noVb+XmZKLL68cjzLsiOAMaA==}
 
+  prosemirror-commands@1.6.2:
+    resolution: {integrity: sha512-0nDHH++qcf/BuPLYvmqZTUUsPJUCPBUXt0J1ErTcDIS369CTp773itzLGIgIXG4LJXOlwYCr44+Mh4ii6MP1QA==}
+
+  prosemirror-dropcursor@1.8.1:
+    resolution: {integrity: sha512-M30WJdJZLyXHi3N8vxN6Zh5O8ZBbQCz0gURTfPmTIBNQ5pxrdU7A58QkNqfa98YEjSAL1HUyyU34f6Pm5xBSGw==}
+
+  prosemirror-gapcursor@1.3.2:
+    resolution: {integrity: sha512-wtjswVBd2vaQRrnYZaBCbyDqr232Ed4p2QPtRIUK5FuqHYKGWkEwl08oQM4Tw7DOR0FsasARV5uJFvMZWxdNxQ==}
+
+  prosemirror-highlightjs@0.9.1:
+    resolution: {integrity: sha512-aqcXUCM4Dbc+0DoORrmF4MWrdIJuaJKUpZvzi1xy0HEx06J5vTlnwR25xCUIbxD3ilOtkabB36QqY3WQ03OuzQ==}
+    peerDependencies:
+      highlight.js: ^11.6.0
+      prosemirror-model: ^1.18.1
+      prosemirror-state: ^1.4.1
+      prosemirror-view: ^1.26.5
+
+  prosemirror-history@1.4.1:
+    resolution: {integrity: sha512-2JZD8z2JviJrboD9cPuX/Sv/1ChFng+xh2tChQ2X4bB2HeK+rra/bmJ3xGntCcjhOqIzSDG6Id7e8RJ9QPXLEQ==}
+
+  prosemirror-inputrules@1.4.0:
+    resolution: {integrity: sha512-6ygpPRuTJ2lcOXs9JkefieMst63wVJBgHZGl5QOytN7oSZs3Co/BYbc3Yx9zm9H37Bxw8kVzCnDsihsVsL4yEg==}
+
+  prosemirror-keymap@1.2.2:
+    resolution: {integrity: sha512-EAlXoksqC6Vbocqc0GtzCruZEzYgrn+iiGnNjsJsH4mrnIGex4qbLdWWNza3AW5W36ZRrlBID0eM6bdKH4OStQ==}
+
+  prosemirror-markdown@1.13.1:
+    resolution: {integrity: sha512-Sl+oMfMtAjWtlcZoj/5L/Q39MpEnVZ840Xo330WJWUvgyhNmLBLN7MsHn07s53nG/KImevWHSE6fEj4q/GihHw==}
+
+  prosemirror-model@1.24.1:
+    resolution: {integrity: sha512-YM053N+vTThzlWJ/AtPtF1j0ebO36nvbmDy4U7qA2XQB8JVaQp1FmB9Jhrps8s+z+uxhhVTny4m20ptUvhk0Mg==}
+
+  prosemirror-schema-list@1.5.0:
+    resolution: {integrity: sha512-gg1tAfH1sqpECdhIHOA/aLg2VH3ROKBWQ4m8Qp9mBKrOxQRW61zc+gMCI8nh22gnBzd1t2u1/NPLmO3nAa3ssg==}
+
+  prosemirror-state@1.4.3:
+    resolution: {integrity: sha512-goFKORVbvPuAQaXhpbemJFRKJ2aixr+AZMGiquiqKxaucC6hlpHNZHWgz5R7dS4roHiwq9vDctE//CZ++o0W1Q==}
+
+  prosemirror-transform@1.10.2:
+    resolution: {integrity: sha512-2iUq0wv2iRoJO/zj5mv8uDUriOHWzXRnOTVgCzSXnktS/2iQRa3UUQwVlkBlYZFtygw6Nh1+X4mGqoYBINn5KQ==}
+
+  prosemirror-view@1.37.1:
+    resolution: {integrity: sha512-MEAnjOdXU1InxEmhjgmEzQAikaS6lF3hD64MveTPpjOGNTl87iRLA1HupC/DEV6YuK7m4Q9DHFNTjwIVtqz5NA==}
+
   proxy-addr@2.0.7:
     resolution: {integrity: sha512-llQsMLSUDUPT44jdrU/O37qlnifitDP+ZwrmmZcoSKyLKvtZxpyV0n2/bD/N4tBAAZ/gJEdZU7KMraoK1+XYAg==}
     engines: {node: '>= 0.10'}
@@ -7278,6 +7367,9 @@ packages:
     resolution: {integrity: sha512-l0OE8wL34P4nJH/H2ffoaniAokM2qSmrtXHmlpvYr5AVVX8msAyW0l8NVJFDxlSK4u3Uh/f41cQheDVdnYijwQ==}
     hasBin: true
 
+  rope-sequence@1.3.4:
+    resolution: {integrity: sha512-UT5EDe2cu2E/6O4igUr5PSFs23nvvukicWHx6GnOPlHAiiYbzNuCRQCuiUdHJQcqKalLKlrYJnjY0ySGsXNQXQ==}
+
   route-recognizer@0.3.4:
     resolution: {integrity: sha512-2+MhsfPhvauN1O8KaXpXAOfR/fwe8dnUXVM+xw7yt40lJRfPVQxV6yryZm0cgRvAj5fMF/mdRZbL2ptwbs5i2g==}
 
@@ -8264,6 +8356,9 @@ packages:
   vscode-uri@3.0.8:
     resolution: {integrity: sha512-AyFQ0EVmsOZOlAnxoFOGOq1SQDWAB7C6aqMGS23svWAllfOaxbuFvcT8D1i8z3Gyn8fraVeZNNmN6e9bxxXkKw==}
 
+  w3c-keyname@2.2.8:
+    resolution: {integrity: sha512-dpojBhNsCNN7T82Tm7k26A6G9ML3NkhDsnw9n/eoxSRlVBB4CEtIQ/KTCLI2Fwf3ataSXRhYFkQi3SlnFwPvPQ==}
+
   w3c-xmlserializer@5.0.0:
     resolution: {integrity: sha512-o8qghlI8NZHU1lLPrpi2+Uq7abh4GGPpYANlalzWxyWteJOCsr/P+oPBA49TOLu5FTZO4d3F9MnWJfiMo4BkmA==}
     engines: {node: '>=18'}
@@ -15702,6 +15797,8 @@ snapshots:
     dependencies:
       readable-stream: 2.3.8
 
+  orderedmap@2.1.1: {}
+
   os-locale@5.0.0:
     dependencies:
       execa: 4.1.0
@@ -16039,6 +16136,81 @@ snapshots:
       retry: 0.12.0
       signal-exit: 3.0.7
 
+  prosemirror-commands@1.6.2:
+    dependencies:
+      prosemirror-model: 1.24.1
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+
+  prosemirror-dropcursor@1.8.1:
+    dependencies:
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+      prosemirror-view: 1.37.1
+
+  prosemirror-gapcursor@1.3.2:
+    dependencies:
+      prosemirror-keymap: 1.2.2
+      prosemirror-model: 1.24.1
+      prosemirror-state: 1.4.3
+      prosemirror-view: 1.37.1
+
+  prosemirror-highlightjs@0.9.1(highlight.js@11.11.1)(prosemirror-model@1.24.1)(prosemirror-state@1.4.3)(prosemirror-view@1.37.1):
+    dependencies:
+      highlight.js: 11.11.1
+      prosemirror-model: 1.24.1
+      prosemirror-state: 1.4.3
+      prosemirror-view: 1.37.1
+
+  prosemirror-history@1.4.1:
+    dependencies:
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+      prosemirror-view: 1.37.1
+      rope-sequence: 1.3.4
+
+  prosemirror-inputrules@1.4.0:
+    dependencies:
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+
+  prosemirror-keymap@1.2.2:
+    dependencies:
+      prosemirror-state: 1.4.3
+      w3c-keyname: 2.2.8
+
+  prosemirror-markdown@1.13.1:
+    dependencies:
+      '@types/markdown-it': 14.1.2
+      markdown-it: 14.0.0
+      prosemirror-model: 1.24.1
+
+  prosemirror-model@1.24.1:
+    dependencies:
+      orderedmap: 2.1.1
+
+  prosemirror-schema-list@1.5.0:
+    dependencies:
+      prosemirror-model: 1.24.1
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+
+  prosemirror-state@1.4.3:
+    dependencies:
+      prosemirror-model: 1.24.1
+      prosemirror-transform: 1.10.2
+      prosemirror-view: 1.37.1
+
+  prosemirror-transform@1.10.2:
+    dependencies:
+      prosemirror-model: 1.24.1
+
+  prosemirror-view@1.37.1:
+    dependencies:
+      prosemirror-model: 1.24.1
+      prosemirror-state: 1.4.3
+      prosemirror-transform: 1.10.2
+
   proxy-addr@2.0.7:
     dependencies:
       forwarded: 0.2.0
@@ -16330,6 +16502,8 @@ snapshots:
     dependencies:
       glob: 10.4.5
 
+  rope-sequence@1.3.4: {}
+
   route-recognizer@0.3.4: {}
 
   router_js@8.0.6(route-recognizer@0.3.4)(rsvp@4.8.5):
@@ -17560,6 +17734,8 @@ snapshots:
 
   vscode-uri@3.0.8: {}
 
+  w3c-keyname@2.2.8: {}
+
   w3c-xmlserializer@5.0.0:
     dependencies:
       xml-name-validator: 5.0.0
diff --git a/script/build_jsconfig.rb b/script/build_jsconfig.rb
index 1e441f3a344..966c3c2bde5 100644
--- a/script/build_jsconfig.rb
+++ b/script/build_jsconfig.rb
@@ -31,6 +31,7 @@ def write_config(package_dir, extras: {})
       "module" => "esnext",
       "moduleResolution" => "bundler",
       "experimentalDecorators" => true,
+      "allowJs" => true,
       "paths" => {
         **namespaces
           .map { |ns, paths| [ns, paths.map { |p| "#{relative(package_dir, p)}/*" }] }
diff --git a/spec/system/composer/prosemirror_editor_spec.rb b/spec/system/composer/prosemirror_editor_spec.rb
new file mode 100644
index 00000000000..64012db13c3
--- /dev/null
+++ b/spec/system/composer/prosemirror_editor_spec.rb
@@ -0,0 +1,290 @@
+# frozen_string_literal: true
+
+describe "Composer - ProseMirror editor", type: :system do
+  fab!(:user) { Fabricate(:user, refresh_auto_groups: true) }
+  fab!(:tag)
+  let(:composer) { PageObjects::Components::Composer.new }
+  let(:rich) { composer.rich_editor }
+
+  before do
+    sign_in(user)
+    SiteSetting.rich_editor = true
+  end
+
+  it "hides the Composer container's preview button" do
+    page.visit "/new-topic"
+
+    expect(composer).to be_opened
+    expect(composer).to have_composer_preview_toggle
+
+    composer.toggle_rich_editor
+
+    expect(composer).to have_no_composer_preview_toggle
+  end
+
+  context "with autocomplete" do
+    it "triggers an autocomplete on mention" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+
+      composer.type_content("@#{user.username}")
+
+      expect(composer).to have_mention_autocomplete
+    end
+
+    it "triggers an autocomplete on hashtag" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      find(".composer-toggle-switch").click
+      composer.type_content("##{tag.name}")
+
+      expect(composer).to have_hashtag_autocomplete
+    end
+
+    it "triggers an autocomplete on emoji" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content(":smile")
+
+      expect(composer).to have_emoji_autocomplete
+    end
+  end
+
+  context "with inputRules" do
+    it "supports > to create a blockquote" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("> This is a blockquote")
+
+      expect(rich).to have_css("blockquote", text: "This is a blockquote")
+    end
+
+    it "supports n. to create an ordered list" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("1. Item 1\n5. Item 2")
+
+      expect(rich).to have_css("ol li", text: "Item 1")
+      expect(find("ol ol", text: "Item 2")["start"]).to eq("5")
+    end
+
+    it "supports *, - or + to create an unordered list" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("* Item 1\n")
+      composer.type_content("- Item 2\n")
+      composer.type_content("+ Item 3")
+
+      expect(rich).to have_css("ul ul li", count: 3)
+    end
+
+    it "supports ``` or 4 spaces to create a code block" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("```\nThis is a code block")
+      composer.send_keys(%i[shift enter])
+      composer.type_content("    This is a code block")
+
+      expect(rich).to have_css("pre code", text: "This is a code block", count: 2)
+    end
+
+    it "supports 1-6 #s to create a heading" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("# Heading 1\n")
+      composer.type_content("## Heading 2\n")
+      composer.type_content("### Heading 3\n")
+      composer.type_content("#### Heading 4\n")
+      composer.type_content("##### Heading 5\n")
+      composer.type_content("###### Heading 6\n")
+
+      expect(rich).to have_css("h1", text: "Heading 1")
+      expect(rich).to have_css("h2", text: "Heading 2")
+      expect(rich).to have_css("h3", text: "Heading 3")
+      expect(rich).to have_css("h4", text: "Heading 4")
+      expect(rich).to have_css("h5", text: "Heading 5")
+      expect(rich).to have_css("h6", text: "Heading 6")
+    end
+
+    it "supports _ or * to create an italic text" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("_This is italic_\n")
+      composer.type_content("*This is italic*")
+
+      expect(rich).to have_css("em", text: "This is italic", count: 2)
+    end
+
+    it "supports __ or ** to create a bold text" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("__This is bold__\n")
+      composer.type_content("**This is bold**")
+
+      expect(rich).to have_css("strong", text: "This is bold", count: 2)
+    end
+
+    it "supports ` to create a code text" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("`This is code`")
+
+      expect(rich).to have_css("code", text: "This is code")
+    end
+  end
+
+  context "with keymap" do
+    PLATFORM_KEY_MODIFIER = SystemHelpers::PLATFORM_KEY_MODIFIER
+    it "supports Ctrl + B to create a bold text" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content([PLATFORM_KEY_MODIFIER, "b"])
+      composer.type_content("This is bold")
+
+      expect(rich).to have_css("strong", text: "This is bold")
+    end
+
+    it "supports Ctrl + I to create an italic text" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content([PLATFORM_KEY_MODIFIER, "i"])
+      composer.type_content("This is italic")
+
+      expect(rich).to have_css("em", text: "This is italic")
+    end
+
+    xit "supports Ctrl + K to create a link" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      page.send_keys([PLATFORM_KEY_MODIFIER, "k"])
+      page.send_keys("https://www.example.com\t")
+      page.send_keys("This is a link")
+      page.send_keys(:enter)
+
+      expect(rich).to have_css("a", text: "This is a link")
+    end
+
+    it "supports Ctrl + Shift + 7 to create an ordered list" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("Item 1")
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "7"])
+
+      expect(rich).to have_css("ol li", text: "Item 1")
+    end
+
+    it "supports Ctrl + Shift + 8 to create a bullet list" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("Item 1")
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "8"])
+
+      expect(rich).to have_css("ul li", text: "Item 1")
+    end
+
+    it "supports Ctrl + Shift + 9 to create a blockquote" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("This is a blockquote")
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "9"])
+
+      expect(rich).to have_css("blockquote", text: "This is a blockquote")
+    end
+
+    it "supports Ctrl + Shift + 1-6 for headings, 0 for reset" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+
+      (1..6).each do |i|
+        composer.type_content("\nHeading #{i}")
+        composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, i.to_s])
+
+        expect(rich).to have_css("h#{i}", text: "Heading #{i}")
+      end
+
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "0"])
+      expect(rich).not_to have_css("h6")
+    end
+
+    it "supports Ctrl + Z and Ctrl + Shift + Z to undo and redo" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("This is a test")
+      composer.send_keys([PLATFORM_KEY_MODIFIER, "z"])
+
+      expect(rich).not_to have_css("p", text: "This is a test")
+
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "z"])
+
+      expect(rich).to have_css("p", text: "This is a test")
+    end
+
+    it "supports Ctrl + Shift + _ to create a horizontal rule" do
+      page.visit "/new-topic"
+
+      expect(composer).to be_opened
+
+      composer.toggle_rich_editor
+      composer.type_content("This is a test")
+      composer.send_keys([PLATFORM_KEY_MODIFIER, :shift, "_"])
+
+      expect(rich).to have_css("hr")
+    end
+  end
+end
diff --git a/spec/system/page_objects/components/composer.rb b/spec/system/page_objects/components/composer.rb
index b5f11aba3f6..fa630e52d97 100644
--- a/spec/system/page_objects/components/composer.rb
+++ b/spec/system/page_objects/components/composer.rb
@@ -5,6 +5,12 @@ module PageObjects
     class Composer < PageObjects::Components::Base
       COMPOSER_ID = "#reply-control"
       AUTOCOMPLETE_MENU = ".autocomplete.ac-emoji"
+      HASHTAG_MENU = ".autocomplete.hashtag-autocomplete"
+      MENTION_MENU = ".autocomplete.ac-user"
+
+      def rich_editor
+        find(".d-editor-input.ProseMirror")
+      end
 
       def opened?
         page.has_css?("#{COMPOSER_ID}.open")
@@ -113,6 +119,14 @@ module PageObjects
         page.has_css?(".discard-draft-modal")
       end
 
+      def has_hashtag_autocomplete?
+        has_css?(HASHTAG_MENU)
+      end
+
+      def has_mention_autocomplete?
+        has_css?(MENTION_MENU)
+      end
+
       def has_emoji_autocomplete?
         has_css?(AUTOCOMPLETE_MENU)
       end
@@ -273,6 +287,11 @@ module PageObjects
         select_kit.collapse
       end
 
+      def toggle_rich_editor
+        find("#{COMPOSER_ID} .composer-toggle-switch").click
+        self
+      end
+
       private
 
       def emoji_preview_selector(emoji)